then how do you know my suggestion (esp use of the cleaner) failed to be the key step in resolving?
Maybe I expressed myself badly before, but I'm just telling you my process in relation to what you advised me. Please don't take this the wrong way, I didn't mean to offend you.
I tried the options you suggested yesterday. Every time I tried an option, I checked if the problem was still there or not. Getting to the last option in the list of suggestions, even after uninstalling and installing Adobe Cloud, it didn't fix it.
Later that day I was involved in solving another problem in illustrator, the problem of links left with yellow box, I searched and found in the community that I had to install the new version of illustrator (27.0.1). It was what I did and that's when I saw that both problems had been solved.
From the process I did, my logic tells me that it was the installation of the new version, but I'm not technical enough to know exactly.