It's amazing to me that someone's whole job could be running the scrum board, and that such a person would be questioning other people's contribution to the team.
"I started work on this item and realized that I'm actually missing a lot of context and information in the requirements. I need your help clarifying them"
The scrum Master knew who to contact to get that information would set up a meeting, have the meeting without me if they thought they could do it or schedule it and include me so I could ask the questions I needed, Mark the ticket for me as blocked, fill out the info after the meeting and communicate the risk and reason for delay to stakeholders.
Basically I could say "There's a problem!" and the scrum Master would get it taken care of or find someone who could. Probably the most valuable person on that team.
On top of that the one I worked with who was good at this also took on small cases because otherwise he'd regularly have nothing to do.