Cisco Anyconnect conection lost after 5 minutes with hex s

Hey folks,

i have a strange issue with my hex s (Router OS 7.8 ). If i work at home office, i use my thinclient (wyse 3040) at home. We connect trough cisco anyconnect vpn (openconnect server).
The problem is, the connection is only usable for 5 minutes…after that i lose the connection to our rds infrastructur, and i have to disconnect the vpn connection in teh thinclient and reconnect..then it wokrs again for the 5 minutes…

Why i know its the hex s ?
Well, if i use my cable modem (vodafone internet) in normal mode and connect the thinclient direct, it works like a charm, if i use my draytek vigor 137 (telekom internet) in router mode and connect directly it works again like a charm.
As soon as i go through my hex s, the issue is back, on both internet connections, regardless if bridge/nat (cable modem), router/modem (dsl modem).

Since we have no ipv6 in our company, and i also dont have ipv6 - exluding cable modem nat mode, i guess thats no the reason, since on the dsl site it works without ipv6 too…

Im a beginner on routeros, so i dont have any clue whats going on here..


Hope some one can help

greetings
Lucky