Speed dial and saved contacts disappearing in Teams calls section

AleksiBe Dear All - I resolved the problem (for myself anyway). 

And no.. I didn't move to Google Office! 8))

Although I am not able to tell you exactly what in the code caused the issue (that's for Microsoft engineering team to figure out), I can say that it has everything to do with local caching of Outlook files .ost/.pst file on your PC:  I can only let you know what my set up is and  what I did that seems to have reliably resolved the issue:

- I run Office 365 latest versions  (I have 32 bit Outlook installed) assuming the issue is the same for 64bit.

- I have multiple email boxes and shares folders that I attach to on Exchange Online. Fairly complex.

- I run the latest version of Windows 10 64 bit. 

I prefer to use Outlook and Teams locally installed on my PC.  This problem started to rear it's head approximately early January 2021 for me.  I went through the normal MS Support channels and although they admitted to knowing there was an issue, they were unable to resolve it - and told me I needed to report the issue on a site the called the "VOICE" in order for the MS Software Engineers to pay attention to it..

Finally 2 days ago because of other issues I was experiencing with Outlook - I decided to:

1. "turn off Caching Mode" on all my mailboxes.

2. Log out of Outlook and back in to Outlook to ensure I was connecting OK directly to the mailboxes at the Online Exchange.  Then I logged back out.

2. I moved my existing cached outlook files to a safe place

    Their location is C:\Users\<your_username>\AppData\Local\Microsoft\Outlook.

3. I then went into "Control Panel" and "Mail (Microsoft Outlook)" ---> "Email Accounts".

4. Change each account to enable local caching again.  This time I told it only to cache 6 months rather than "unlimited" which is what I had before.. (Maybe 1 year, 2 years would work also .. I just have not tested that).

5.  Restarted Outlook and gave it a chance to re-create fresh cache files.

6.  I then started Teams and decided to leave it running and test for 24-48 hours during which time I would test it.  

The problem had disappeared.  and it seems almost like Teams is performing a bit better.

So there you have it.  The above is what has eradicated the issue I had with my "Speed Dial Contacts disappearing intermittently".  So far I have gone 48 hours with Teams running locally and (knock on wood) the speed dial contacts have been stable.

I hope this helps.