Hello! I'm gonna quote Kiki from a similar threat.
Welcome back!
Make sure to not minimize your browser (minimized browsers may cause the login tab to log you out)
Clear caches/history
Enable cookies
Disable proxies
Try another browser
Log in from a mobile device
Restart your router
Let us know if you need more suggestions~
Also make sure you don't close the tab when you log into it. If you x-out of it, it will log you out. After you log in, you're gonna have to wait a little bit, and then it should let you in.
I hope it helps!
(https://snag.gy/gM5PLC.jpg)
This is what pops up when I attempt to log in.
It looks like you have a older version of FeralHeart, if I'm not mistaken. The update log is of the old download, and doesn't have anything current. Not to mention you have the old Watermill map on the load screen, as well as old interface textures (not unless you've replaced everything like I have). You'll have to download the updated version of FeralHeart, and it should work.