Return of Reckoning

Hello,

I can't currently access Abilities and Backpack windows, the rest of UI (Character screen, Main menu etc) are working normally. Any ideas for a reason/solution or should I just try to reinstall and hope for the best?

Try keybinding those windows again. P for char window, maybe I for inventory? B is just too conveniently placed not to use it as combat keybind.
Skills window I just click on top menu, V is "fast combat key" as well

Gud huntin'

Mostlikely your client was not patched fully. Restart your launcher several times, that should fix it.