I have the same issue.
I logged out of the forums on my phone and when I logged back in, of my 14ish characters, only four are available to choose from. Worst of all, my posting charater isn’t one of the options.
It’s the same on every device (phone, desktop, laptop). Luckily I haven’t logged out on my PC, so it’s still is set to my posting character.
(This is Leviathan)