I cannot see comments made by lemmy.world instance when logged in to discuss.online. Not sure if any other instances are affected this way. I also cannot search some communities. I have not figured out a pattern. I wonder if it is intentional. Here is an example: https://discuss.online/post/202378. There are a few comments under the post, but I do not see them.
For example, if no one on discuss.online was subscribed to https://lemmy.world/c/gamingsuggestions at the time https://lemmy.world/post/943892 was posted, there will be no comments federated to https://discuss.online/post/202378. Once a user on discuss.online subscribes to https://lemmy.world/c/gamingsuggestions, only posts and comments from that point forward will be federated.