This sounds similar to a bug we found just before the olive release, where changes were only saved if the text was changed. If your edit only changed markup (for example, adding a link or changing styling) it wouldn’t be saved.
However, this was fixed before the olive release in https://github.com/openedx/edx-platform/pull/31212 (there’s a video recording demonstrating the issue on the pull request).
How did you upgrade to Tutor 15.1.0?
Are you using the new Text editor? (have you turned on the waffle flag ``new_core_editors.use_new_text_editor?)
Peter Pinch
MIT Open Learning
he/him/his