Is there a limit to the amount of sheets that can be a source for a report?

I use two reports to consolidate high level risks and issues for projects across my team. However, we are running into issues where sources seem to be disappearing.

Is there a limit to how many sources a report can pull from? If so, what is it?

One report has 12 sheets, and the other has 9. Is there potentially another reason that folks' sources may not stick over time? Are my team members somehow overwriting each other?

Help! :-)