You might consider setting up some type of monitoring for it temporarily
I've had a similar issue a while ago that was caused by a memory leak in Exchange itself. It kept consuming more and more RAM and at the end of the day crashed the whole VM with a blue screen. It was happening like once a week usually on weekends thus I didn't pay too much attention to the issue since nobody complained. However, it got worth with time so I had to investigate what is actually going on and take measures like adding more ram, defragging the DB and so on.
Drop some monitoring agent inside the Exchange VM like Veeam One Monitor to be able to understand what's going on or choose something from the recommended tools here.