Please look in this thread, perhaps it should have gone here. Grüße vom Sänger ♫(Reden) 08:10, 31 January 2017 (UTC)
P.S.: The incident happened with a current FF under Mint.
Topic on 2017 wikitext editor/Feedback
I added your details to the current task.
It just happened again, this time 605 KB ;)
It seems to be, that if I edit a section, get an edit conflict in there, and try to resolve it, the 2017WE thinks the section is the whole page and ditches the rest.
Like, consistently? We're looking for ways to reproduce this, if this is one I can add it to the task.
I never tried it again in the real world, as I feared it would happen again. This was the first time I dared, and voila, it struck again, so: yes, probably a pattern.
As an answer to Anomie over @Phab:
Not that I know any daft thing about API, but your reasoning reads reasonable ;)
I just had an edit conflict while editing the whole page, and it jumped back to the normal editor, and the normal diff-view inside this for edit conflicts. Nothing was lost.
IIRC there was no such thing as the normal diff-view in the normal editor after the edit conflict while I edited just the section. Grüße vom Sänger ♫(Reden) 17:46, 3 February 2017 (UTC)