Hello, I have the same problem (WP 6.5.5). I believe, that the problem started with update to 6.5.5. I have 97 marker in the map, can add marker, but cannot insert any text in the marker. Existing marker I cannot change. Is there a marker-limit?
I opened a new block on a separate page: here I can add marker and fill in the text. As a workaround I copied the data from the database and fill in the markers new. At the moment i am at marker 40.
regards Peter