This is very interesting to me as I was getting crashes when exiting games too, but was unable to get any help here which resulted in me having to quit using Recalbox sadly. I notice that in my .ogg collection on my install that I have four files with a higher sample rate than 44.1Hz. I will redo these and see if it gets the system stable again.
Thanks for posting your advice. I will post back if this works.
Pardon my b*mping of this topic but I think this may still be an issue for some users.
I have discovered the solution here. It turns out that I had 4 music tracks that were sampled at 48000Hz rather than 44100Hz, and this was causing the crashes. Remedying this has fixed the problem. Hope this comes in useful (and pops up in Google searches!). 
Well, just spent over an hour testing with the changes made to my background music, and yes it would seem that this fixes it! To say I am extremely pleased would be an understatement. I'm absolutely thrilled!
Thank you for posting the solution. I cannot wait to get back to Recalbox.
Sorry, it would need to be Linux based or at least compatible with WINE. I don't use Windows. Thank you for the suggestion though.