I have exactly the same problem. The guest os keep crashing from time to time. I have CentOS guest machine and another Windows 2012 machine and they are crashing from time to time.

The host is an iMac 27 inches with 64 GB RAM, CPU i5 4 cores and external SSD. 

I checked your log file and it's similar to my log file , where this is a PANIC:

2021-01-31T17:32:13.534+03:00| mks| I005: SOCKET 1 (61) recv detected client closed connection
2021-01-31T17:32:13.534+03:00| mks| E001: PANIC: ISBRendererComm: Lost connection to mksSandbox

Please check my attached log.