HI Beatrix, From case 60743, Stephane’s final comments show it was not reproducible. Like I mentioned when we emailed about this earlier, I have been keeping a file on anyone who has had this issue. And though I helped about some people after they initially upgraded to Catalina, but no one else has reached out having the same issue you are. There are less people who switch between releases like you do, but if we could get details from others that would be really helpful in tracking this down.
All this said, any issue with activation and licenses is something I take seriously and want to fix. My understanding is that an older release may be using a different identifier, which can cause issues with switching between 2020r1 and 2019r3, on say Big Sur which wasn’t around when 2019 was released. (I say this with big “I am not an engineer” caveats). @Jeff_Tullin, please let me know if this happens to you again now that you have activated on Catalina. And @Beatrix_Willius, If you continue to encounter this, please contact me at firstname.lastname@example.org the more info I have the better. I am actively tracking this and have talked with engineers about it.