If someone replies while a thread is loading that reply won’t show up even if you get the notification. Refreshing the page doesn’t work, the only way to see the reply is by leaving the thread then re-enter it.
You need a new phone. No joke, get a new one or a replacement through your service provider.
You can do a factory reset on the phone, and see if that helps anything.
At this point it must be something with your device because no one else has the majority of the problems you seem to be having on the Forums.