I have the same problem, and I checked the other possible solutions, but it didn't work (create a new addon.xml on /storage ... Set a delay for the connection, etc). The other repos work fine.
I think that the link of my addon.xml points to nothing (or not the right one). (Sorry I cannot access it right now, I'll provide the file later if you need it)
I run libreelec 9.2 on a olinuxino-a64 (olimex). What changes should I make to the addon.xml in order to access libreelec addons ? (Or, is there something forgotten in the webserver?)
Thanks for your help