>>Had this in the last 4 days:
>>was logged in in FF,
>>looked something up on tablet without logging out on PC
>
>Do you mean you switch to another device to log also to UT?

yes, Nexus tablet with Dolphin browser

>
>>back on PC my session was removed by second log in
>
>Do you mean on your original session, the login was no longer recognized and you were forwarded to a login page?

yes, login page was shown but after that login the blank page happened. After next login, usual page was shown.

FF 43.0.3