Users can connect to Minecraft server but time out during terrain download
. My theory is that you (the remote host) don't have a strong enough connection to ensure that other users (besides you) can connect to the server properly. Try running an internet speed test. If you internet is normal/fast, other people's connection might not be good enough to download all the server data. Try reducing the amount of server data that other users have to load ( for example clearing blocks, removing various particle effects) or otherwise getting a better internet connection or asking your friends to do so.