I have created a ticket with Microsoft Support but it's been 6.5 weeks with no solution, so I'm hoping someone else has experienced a similar issue and can help me here.
New users in our environment are seeing UTC values for User Local datetime fields for Events that were created before the user accounts were created. I have changed the affected users' timezone from Eastern to Central and back to Eastern, with no luck. This has happened to a few users previously, but it always just worked itself out after about 1 week. Based on my research, it could be a delayed timezone hydration issue that Microsoft needs to reset/resync, but I'm hoping it's something we can fix on our end instead.
Thanks for any help/insight!