You seem to be having some rather strange issues it would seem. Most of these do not happen to me.
I know about the letters, and yes, there's not a way around that really, but as for some of the others, let's say Fluorite Plains crashing, try entering from the Cape-side more often, there are usually less people there.
If material files aren't saving, that's nothing to do with FeralHeart really.
Everyone gets a bad token every now and then. FeralHeart averages a lot of users online, it's not going to run perfectly for anyone.
And as for posting, it often tells me this too, "Your session timed out while posting. Please try to re-submit your message. I found a simple way to fix that.
In a new tab, open "Logout"
Then log in to the orange box. Close that tab once logged in again.
Back on your post tab, "Post" again. It will fail. "Post" once more, it will go.
Tedious, yes, but it works.
Now I'm not saying the game is totally perfect either, no, I agree with what Red said in the aspect that it needs improvement, but maybe we can fix some of your issues with this game. c: