IPSec issues

Hello,
can someone with more ipsec experience can help to figure out random IPSec issues?
What is the reason for a reschedluingevent ?
Sometimes 2 or 3 from 20 local users where disconnected from her VDI Remote Desktop based on a pcoip Protokoll connected via IPSec. It looks like a phase 2 issue but I have no access to the connected Fortigate firewall to look inside the logs.
ipsec_issues01.jpg
and
ipsec_issues02.jpg
Thanks
Maedo