Because the account IP is binded. when user login with different IP, old session will be expired.
Ah this explains it. Yes new times are horrible.
I have 3 locations with Wlan where i am, all with a DSL connection. and these public dsl conections are chaning IP usually all 6-12 hours
And during movement between locations, i am connected 3G or LTE - and even between 3G and LTE i am given a differnt IP....
mabye you fix this soon.
Thx.
One thing, i am always very frustrated with your interface
When drawing a line or so, you can only start "at a point in the curve" -- except the future side
Feature:
- Drawing Lines "free without point-bonding"
- Line Drawing "maybe holding shift" doing a horizontal one ?
- Line movement when drawn (x-y movement ( rotation ?)
- Zoom Feature, so that when you "draw" outside the view you are seeing where you land
Can't you do these features for "premium" users only ?

Now login with different IP is supported. and added a new option 'Close other sessions'.
Press Ctrl to draw free lines, it was added long time ago but didn't public yet.
Press shift to draw horizontal line was considered too. it should be no problem to support it.
About Line movement when drawn, I'm sorry I could not understand it.
About Zoom feature, it needs some more time to test.
-- UPDATE --
'Close other sessions' in login page is removed. It is moved to new user control panel 'sessions'.