The add-on exported one of my lists of places, but when trying to import in Google My Maps I got an error message saying "The file contains invalid or unsupported data, or the file is too large to parse". The list had only 51 places. The developer suggested to try to verify the GPX file using the free gpx.studio web app, and it indeed worked, the file was OK. I then exported the POIs list using the gpx.studio, and the new file was recognized and opened by Google My Maps. So, what should I do next? Should I use 2 apps to get a readable GPX file by Google My Maps? My understanding is that the GPX file exported by this add-on still has a small problem which is tolerated by gpx.studio and may be corrected by it. If the developer could correct this problem, it would be great. I have to mention also that I tried importing the GPX file generated by this add-on in an Android app and it didn't work, but the exported GPX file by the gpx.studio web app was imported fine by the Android app. I apologize for writing all this here, but I couldn't find other way to connect with the developer.

Works fine. Refresh an already open list and have no locations open then run the extension.
Edit: did work, now it doesn't on the same / new lists.