OpenHAB crashes every Saturday and Sunday 0 AM

I am running OH on Synology.
One rule is active and regulates the thermostates.
The rule is only active MO-FRI. (code below)

OpenHAB runs stabel throughout the week.
But, precicesly at SAT 0 AM the system becomes irresponsive.
Basic and Paper UI can still be reached on the server through the web interface.
But buttons are not responsive and values no longer update.
Restart on SAT morning resolves the issue until precisely SUN 0 AM.
Then MO-FRI runs find again.

CODE:

rule "WeekGoodMorning"
when
Time cron "0 0 5 ? * MON-FRI"
then
{
kueche_maxSetTemp.sendCommand(20)
room1_maxSetTemp.sendCommand(20)
room2_maxSetTemp.sendCommand(20)
schlafzimmer_maxSetTemp.sendCommand(20)
bad_maxSetTemp.sendCommand(20)
}
end

rule "WeekGoodMorningOff"
when
Time cron "0 0 7 ? * MON-FRI"
then
{
kueche_maxSetTemp.sendCommand(19)
room1_maxSetTemp.sendCommand(18)
room2_maxSetTemp.sendCommand(18)
schlafzimmer_maxSetTemp.sendCommand(18)
bad_maxSetTemp.sendCommand(18)
}
end

rule "WeekGoodNight"
when
Time cron "0 30 16 ? * MON-FRI"
then
{
kueche_maxSetTemp.sendCommand(20)
room1_maxSetTemp.sendCommand(20)
room2_maxSetTemp.sendCommand(20)
schlafzimmer_maxSetTemp.sendCommand(20)
}
end

rule "WeekGoodNightOff"
when
Time cron "0 20 19 ? * MON-FRI"
then
{
room1_maxSetTemp.sendCommand(18.5)
room2_maxSetTemp.sendCommand(18.5)
schlafzimmer_maxSetTemp.sendCommand(18.5)
}
end

rule "WeekGoodNightRestOff"
when
Time cron "0 00 22 ? * MON-FRI"
then
{
kueche_maxSetTemp.sendCommand(18.5)
arbeitszimmer_maxSetTemp.sendCommand(18.5)
}
end

I removed all rules but the issue remains. OH stops being responsive SAT and SUN 0 AM.

I had a similar issue with astro-binding, which stopped working after a few days in OH 2.0 . I than made a scheduled restart of OH in /etc/crontab every wednesday and sunday morning as work-around. I have to analyse if that is still necessary in OH 2.2.