Alright, quick update on @Hangman's comment: your document did open correctly, but as you indicated, is quite a mess. All of a sudden I have a huge amount of masters en and there were a lot of doubles. I choose not to recover, but incrementally alter, save, close and reopen the file. The problem did seem to come from page 41 and it seems to be one image that did not sit right for some reason. It's an asset I have copied and pasted from Affinity Designer, like many others, but apparently this one created the crash. Rather than past as content I now used the 'place image' and that worked.
I'm now on the road to recover and further the file from the latest version. Hopefully I will never see this behaviour again. It is very jarring that a complete program crashes on a file that I'm editing, but I do understand software development, so I understand weird stuff happening.
Thanks for the tip and the effort.
Cheers!