Apparently something to do with snapping...
The attached video shows me moving a selection of text a little, saving (successfully), then moving the same text a little more, incurring various snapping lines, saving and crashing. Two of the several crash logs attached as well as the original file.
Affinity Designer_2019-09-03-101402_SpamBook2018.crash
Affinity Designer_2019-09-03-101740_SpamBook2018.crash
Screen Recording 2019-09-03 at 10.18.21 AM.mov
bockanalia_1.afdesign