Outlook 365: Duplicate conference room names showing under locations

I'm updating this post after spending most of the day troubleshooting through trial and error. Like many of you, we were also experiencing duplicate room names. Even though we operate in a hybrid environment, our rooms exist only in O365.

I initially tried clearing caches, deleting registry keys, resetting calendar caches, and removing suggestions in OWA, but none of these resolved the issue. Eventually, I discovered that the duplicate room entries had outdated legacy email references listed under their UPNs.

To fix this, I removed all the old email references, keeping only the primary SMTP address, the Office 365 email address, and the SIP email address. After making these changes and waiting a few hours, the issue was resolved! (Images below to help anyone needing visual assistance).

I hope this helps the community—it's not immediately obvious that this would cause the issue we experienced.