can’t update posts anymore + strange HTML inserts

Hi :)!
As of today, I can no longer update already published posts, which used to work fine before.
I merely was going to fix some typos, so I went ahead and made the corrections, hit “update” as usual – and nothing happened.
Even after clearing the complete cache (browser and wordpress caching plugin), nothing.
The strange thing is that after the success message “post updated”, when I go and check the post and then come back to edit it again, the changes are no longer there (as if they were never saved in the first place).

What’s really strange: I noticed that something inserted weird things into the HTML code at every typo that I was going to correct. I’m using grammarly, which never gave me any problems.

Here’s an example of the “weird code”:

<g class="gr_ gr_3 gr-alert gr_gramm gr_inline_cards gr_run_anim Punctuation only-ins replaceWithoutSep" id="3" data-gr-id="3">and</g>

this is apparently about a recommended comma before the word “and”.

How does this all fit together?
Are those issues at all related?

Any suggestion would be greatly appreciated :)!

Thanks!