Hi guys,
we are experiencing the same problem!
our system:
OS Server: SLES 11 SP4
OS Client: Windows 10 Enterprise 64 bit
Server: 5.7.1 (initially 5.1-> 5.4 -> 5.7.1)
Client: mostly mattermost desktop app 4.2.0/4.2.1, no browser
Sessions (LDAP/Mobile/SSO): 30 days
Session Cache: 10 Min
our mattermnost runs behind nginx. Configuration as described here:
https://docs.mattermost.com/install/config-proxy-nginx.html
Summary (exactly the same behaviour as descibed by Camille and Schrell):
User will become logged into another user’s account somehow, either over time or immediately after logging in.
all users were set up the same way.
after client start the user is automatically logged in as another user (sporadically!) so you can read the whole communication(posts/channels etc.) of the affected colleague.
sometimes it is enough to click on File -> Settings… -> server name and then you are magically logged in as another user
it is difficult to reproduce the issue because very offen it is working as expected.
the affected users have only one account. Our working stations are new and without “history” so there is only one user profile
currently there is only one workaround: “clear cache and reload” and then it just works.
There is nothing suspicious in the log and i have no guess what is going on and the project leads are getting nervous. 
Any Ideas for further investigations?
Thanks in advance
Roman
