This is strange, @b-d - we'll look into this and see if we can't identify a fix.
Hang tough!

Please have the users uninstall/reinstall the app. Let us know if issue is still the same .

Many users in our company are also reporting this problem. Profile
pictures are randomly changing to another user's profile picture.

I wonder if one can simply add a profile picture (avatar) to their account. Since this is only happening to people without profile pictures, adding a profile picture to the account should solve the problem. If one still wants to use just their initials, they can use this:
https://google-avatar.herokuapp.com/

Update from this morning (4/5/21 0900):

Hi,
The issue that you have reported in this ticket is related to a Known Issue/Bug we currently have in our system.
JIRA: RCM-8902 | User without avatar in RCM shown with avatar of another user
At this point, we will be placing this case into a PKI Hold status. PKI stands for Product Known Issue. This means that we are investigating it as a bug on our side and there is no currently available ETA when it will be resolved. We have reproduced the issue and are working on resolving it. You will not receive much in the way of correspondence while they resolve this issue, however you will be notified when the issue is fixed.
Thank you for your patience.
Regards,
RingCentral
Tier 2 Support

@andymWe are having the same issue, and it is happening with users that does have avatarpersonal photo. not only users who doesn't as explained on the JIRA above. this is serious issue that it will need to be fixed ASAP please. Thanks!