I upgraded my firmware of both routers to the latest version. Then I converted over to an AIMesh configuration. The router performance was unusable. Tried ASUS support without any progress. From a comment on this forum, I then did the factory reset suggested. It solved the problem and I got the AIMesh working at high speeds.
So do not forget to do a factory reset - probably after every version upgrade with these ASUS routers.
So do not forget to do a factory reset - probably after every version upgrade with these ASUS routers.