Howdy mightymen,
This is funky. Thanks for posting all of your testing and steps to reproduce. That really helps.
Would it be possible for you to test if this if this is something on your site that might be conflicting. This guide will walk you through that short process. If something is, it then walks you through identifying what is conflicting. Once we know that we can work towards a fix. Specifically when testing, try recreating an event and seeing if the date is still wrong. It is likely that events which already have the wrong date will stay wrong even after we find a fix, so they can be ignored/deleted.
Please let me know if you have any questions along the way. Cheers!
– Brook