Find and Replace 2.1.49, 52, 53 (Bug)

I am trying to use Find and Replace to do the following replacement (to shrink images in batch):

It works fine for some notes, but it has no effect on others; both if I specify a field or not, no matter how many times I try.
But: by opening and closing the HTML editor of a note (in whichever field), then running Find and Replace again, this time it will function correctly on that note.
Similarly for multiple notes (taken from the group F&R didn’t work on the first round): all the notes of which I opened and closed the HTML editor will be edited, all the others will not.

This happens both in Anki 2.1.49, 2.1.52 qt6 and 2.1.53 qt6 (beta)

The editor normalizes HTML when it displays it. You can export to a text file to see the original HTML - perhaps some of your image tags actually look like <img src="foo.jpg" /> or similar.