System crashes randomly

dear all

For some time now the system crashes sporadically. First of all, in order to start debugging: where could I find some useful information in the log files. In openhab.log I don’t find anything useful. In syslog I have found the following:

Jul 13 07:52:55 openHABianPi karaf[722]: at java.util.concurrent.ScheduledThreadPoolExecutor$
Jul 13 07:52:55 oJul 13 07:17:03 openHABianPi rsyslogd: [origin software="rsyslogd" swVersion="8.4.2" x-pid="434" x-info=""] start
Jul 13 07:17:03 openHABianPi systemd[1]: Mounted FUSE Control File System.
Jul 13 07:17:03 openHABianPi systemd[1]: Mounting Configuration File System...
Jul 13 07:17:03 openHABianPi systemd[1]: Starting Apply Kernel Variables...

with all the start up information followed (side note: with start up time is changed from 07:52 to 07:17, why?)
start up is ending with

Jul 13 07:17:10 openHABianPi systemd[1]: Startup finished in 2.684s (kernel) + 10.644s (userspace) = 13.328s.
Jul 13 19:35:12 openHABianPi systemd[1]: Time has been changed

So, system was somehow blocked till I restarted at 19:35.
My questions:

  1. Has anybody an idea where I could find more useful log information?
  2. has anybody an idea what the cause of these crashes could be?

btw: I’m on the latest openhab2 version (2.3). Among others I have installed modbus and ebus bindings.

Many thanks in advance for any hints

Best regards