@olivierlambert I was experiencing the same problem on a centos8 host. I could always reproduce the crash by triggering an rsync of a 10GB folder. I was also getting these lines in /var/log/xensource.log
Nov 16 17:46:30 bm-ve-srv02 xenopsd-xc: [debug|bm-ve-srv02|39 |Async.VM.clean_shutdown R:2f7f9c937513|xenops] Device.Generic.hard_shutdown_request frontend (domid=37 | kind=vif | devid=1); backend (domid=0 | kind=vif | devid=1)
I could workaround it by setting a fixed value for memory as suggested in post https://xcp-ng.org/forum/topic/4176/vm-keep-rebooting
In the "Advanced" tab for the VM I had "Memory Limits >> Dynamic 2GB/16GB"
I have changed it to "Memory Limits >> Dynamic 16GB/16GB" and the machine doesn't crash anymore when I trigger the rsync.