Deep Links not working when the userPricipalName has uppercase letters

We have been trying to use teams deeplinks
https://docs.microsoft.com/en-us/microsoftteams/platform/concepts/build-and-test/deep-links

Only the call and chat ones, found that for some users where the userPricipalName is sentence case e.g. Joe.Bloggs@mycompany.com the call deeplink fails but the chat one works fine.
Found for a a few users where the userPricipalName is all lower case the call and chat works as it should. I have tried putting the email all lower case in the deeplink but this return the same message "There's a problem with the link
Try contacting the person who shared it."

The users are syncd from on prem AD to Azure AD.

As the chat link works fine, I'm reluctant to update AD userPricipalName to lower case to resolve the issue as it looks as though something different occurs on calling the call deeplink than the chat one.

I can't see any other reports but guessing that may be down to limited use of deeplinks, our use case is to promote the use of teams.

Anyone experienced anything similar?