I reported this issue first on the PhD forum but Andy says it appears to be related to the SGP guider API so am re-posting it here:
The debug logs indicate the crash happening right after the exposure request is issued to the SGP API guider, so I think we need to have Main Sequence Software look at it first. They will need to see your SGP log.
FYI, this is all with the 18.104.22.1681 version of SGP, not the 2.4 beta.
I had originally downloaded the current development build of PhD 2 as well as the current SGP guider API in order to test the new comet tracking in PhD. Once I was done with the comet, I went to a conventional object and conventional guiding and had repeated PhD 2 crashes not long after guiding was asked (by SGP to PhD) to start. I uninstalled the current version of PhD and went back to 2.3.1i (which has been stable for me) and it still crashed with that. Finally I also uninstalled the new SGP API and went back to the old version of the API (V 1.1.0). It now works properly again with no crashes.
FYI, the crashes DID NOT happen when I was testing the PhD comet tracking, probably because I was doing manually triggered images with frame and focus and was manually starting and stopping guiding from PhD. It only happened when SGP was commanding the guiding to start and stop as part of a sequence.