This bug was filed from the crash reporting server and is br-b8a90a9e-6a02-4e56-9d07-4e5d64933260.
I'll be darned, it's crashed a second time the same day. This time the Slide Master showed a (incorrectly sized) Portrait orientation, yet up to now everything has been Landscape.
All I was doing was to check the Master had a Footer and was the showing Slide Number- I ticked the boxes and thereafter the Slide was shown as Portrait then it crashed.
Again, Recovery was OK but I did not dare try to reproduce the problem.
Impress 18.104.22.168 (x64)
Hey, I see there are many later versions of Impress in the drop-down list on this page - how come the update system hasn't updated mine yet?
5.2.7 is the last version of 5.2 branch.
For the moment, update system won't propose update of a more recent branch.
5.2 branch is EOL so please give a try to last stable LO version 5.3.4.
If you reproduce the crash please revert back status to UNCONFIRMED.
I reported a similar bug 111308