When I try to resize the sidebar it starts flickering / moving very fast between two sizes. The mouse pointer freezes, I can still move it, but cannot click anywhere. Not in Libreoffice nor anywhere else. Keyboard works, Libreoffice must be killed by terminal.
Thanks for reporting. Installing additional icon themes (like I suggested in Bug 93677) should prevent this from happening in many cases. There is also a fix for additional case in Bug 93290, which should be part of the 5.0.1 release. And finally - a global fix that should (hopefully) prevent any such cases in the future is in Bug 78111, and will be in the 5.0.2 release.
*** This bug has been marked as a duplicate of bug 78111 ***