problem with game sharing

My brother shared his account with me, including his games, and I set his account as my primary PS5. It worked; I was able to install the games and play them for a few days. However, yesterday, when my brother tried to launch a game on his PS5, he couldn't because it said there was a licensing problem. He switched his account back to primary on his own PS5, and everything worked again. Is this a sharing issue or something else? Is there a way to fix this? Sorry if some of the words are incorrect; I'm not a native English speaker and had to use Google Translate.