According to the Scrum Guide, an impediment is any factor that blocks or slows down the Developers in their creation of a valuable piece of software in a Sprint, or that restricts the team in achieving its intrinsic level of progress1. Therefore, the scenarios that are impediments are:
A team member talking about a user story that is not on the Scrum board: This indicates that the team is not focused on the Sprint Goal and the Sprint Backlog, which are the sources of alignment and commitment for the Developers. Talking about a user story that is not on the Scrum board can also cause confusion, distraction, and waste of time for the team2.
A technology that blocks agile capabilities: This implies that the team is facing a technical issue that prevents them from delivering a potentially releasable Increment of value at the end of the Sprint, or from collaborating effectively with the Product Owner and other stakeholders. A technology that blocks agile capabilities can also hinder the team's ability to inspect and adapt their work and process3.
A lack of team empowerment and an inability to self-organize: This suggests that the team is not able to make decisions and take actions that are best suited for achieving the Sprint Goal and delivering value to the customer. A lack of team empowerment and an inability to self-organize can also affect the team's motivation, creativity, and productivity.
The scenarios that are not impediments are:
A team member talking about a user story that is on the Scrum board: This indicates that the team is engaged in the Sprint work and is discussing the details and progress of a user story that is part of the Sprint Backlog.
Talking about a user story that is on the Scrum board can also foster communication, collaboration, and transparency within the team.
A review of the backlog at daily standup meetings: This implies that the team is using the daily standup meetings as an opportunity to inspect the Sprint Backlog and adapt their plan accordingly. A review of the backlog at daily standup meetings can also help the team identify any impediments or risks that may affect their Sprint work.
1: Scrum Guide, November 2020, p. 9 2: The Scrum Master as an Impediment Remover, Scrum.org, April
2016, 1 3: Navigating Impediments, Scrum.org, October 2020, 2 : Solving Impediments as a Scrum Team, Scrum.org, August 2018, 3 : Scrum Guide, November 2020, p. 10 : Scrum Guide, November 2020, p. 11

project manager who is acting as a servant leader should empower the team members to conduct their job activities and hold each person accountable to improve the schedule. This is because a servant leader demonstrates commitment to serve and put other people first, and emphasizes flexibility and empathy to empower team members to adapt and thrive. A servant leader also fosters a culture of collaboration, communication, and feedback, and helps the team members develop their skills and potential. By empowering the team members, the project manager can improve their performance, motivation, and satisfaction, and ultimately get the project back on track.
The other three options are not the best actions for a servant leader to take, because:
Notifying the project sponsor that the team is underperforming and requesting additional resources to compress the schedule is a possible option, but it is not the first thing to do. The project manager should first try to address the root causes of the team's low performance, and explore other ways to improve the schedule, such as fast-tracking, crashing, or re-baselining. Requesting additional resources may not be feasible or effective, and it may also undermine the trust and confidence of the team members and the sponsor.
Contacting each team member to inform them that further schedule slips will not be tolerated by the project sponsor is a coercive and authoritarian action, which is contrary to the servant leadership style. This action may create fear, resentment, and resistance among the team members, and damage their morale and engagement. It may also increase the risk of conflicts, errors, and turnover, and worsen the project performance.
Beginning holding daily meetings to assign each team member discrete tasks with specific due dates is a micromanaging and controlling action, which is also contrary to the servant leadership style. This action may reduce the autonomy, creativity, and ownership of the team members, and make them feel disempowered and demotivated. It may also increase the workload and stress of the project manager, and hinder the team's collaboration and learning.
References:
Leadership Styles - BrainBOK
7 Traits of Servant Leadership in Agile Project Management - Project Management Academy Servant Leadership in PMO Management: A Path to Success - IIL Blog Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition. Project Management Institute.
Project Management Institute. (2020). Agile Practice Guide. Project Management Institute.

The project manager should conduct a meeting with the project team to discuss and address the sources of disagreement, as this is a strategy for improving team morale and performance. According to the PMI website, one of the interpersonal and team skills that a project manager should have is conflict management. Conflict management is the process of resolving or reducing disagreements among project stakeholders, such as team members, sponsors, customers, or suppliers. Conflict can arise due to various factors, such as personality differences, communication barriers, resource constraints, or competing interests.
If not managed properly, conflict can negatively affect the team morale, productivity, quality, and satisfaction.
The project manager should use appropriate conflict resolution techniques, such as problem-solving, compromising, collaborating, smoothing, or forcing, depending on the situation and the desired outcome. The project manager should also facilitate open and constructive communication, encourage feedback and participation, and promote trust and respect among the team members1. By conducting a meeting with the project team, the project manager can identify the root causes and the impact of the disagreement, and work with the team to find a mutually acceptable solution. The project manager can also clarify the project objectives, scope, and requirements, and ensure that the team members understand their roles and responsibilities. By addressing the sources of disagreement, the project manager can improve the team morale and performance, and get the project back on track.
The other options, informing the stakeholders, crashing the project timeline, or issuing a change request, are not the best ways to deal with low team morale and disagreement. Informing the stakeholders may be a necessary communication activity, but it does not solve the problem or improve the situation. Crashing the project timeline may be a schedule compression technique, but it may not be feasible or effective, as it may increase costs, risks, or rework, and may also worsen the team morale and satisfaction. Issuing a change request may be a change management activity, but it may not be necessary or desirable, as it may imply that the project manager is unable to manage the project within the agreed baselines.
2 Interpersonal and Team Skills - Project Management Institute 1 A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Sixth Edition, Chapter 9.5

In an agile project, it's important to manage ad hoc requests and meetings effectively1. When the project owner repeatedly calls for ad hoc meetings, it can disrupt the team's workflow and productivity2. Therefore, the project manager should coach the project owner about the implications of unplanned meetings1. This includes explaining how these meetings can affect the team's focus, productivity, and the overall project timeline1. The project manager can also suggest alternative ways to communicate or schedule these meetings in a way that minimizes disruption to the team34. References:
https://www.projectmanager.com/blog/project-meetings-for-your-team
https://www.range.co/blog/ad-hoc-meetings