It took me personally 4 tries to enter the game. I tried 2 times to register, and when tried to log in it said the password was wrong (even when it wasn't). Closed the game, Then tried to enter as guest - and it did not let me.

After the second closure, I clicked on enter as guest and it did finally let me.

Also tried the lamb mission. action wouldnt work! and the Property of BBC was anoying on the demo! why would they do that?!!

I had this issue the first 2 times. I signed in as guest, played for a little bit, got an error about memory allocating, got kicked off game. I played as guest 3 more times then tried signing in with an email. The email already had an account, but I didn't know password, so I registered with a new email. Got in fine, username and password are saved but I keep getting kicked off with this video memory error.

Clicking register went to just a blank screen that you could hit esc on and go back to the previous menu.

I also had a similar issue where the register button was not responding. I thought it may be AdGuard Home(so I disabled it temporarily) blocking access to the servers. I also tried another password without the plus symbol (+), but then when I tried to register again, it said username already taken, so I re-enabled AdGuard and I tried to login with my original password and got logged in. Not sure if it's combination of AdGuard, password characters, or server/other issues.

When I tried registering, I was able to fill out the requested fields but then after clicking the Register button, nothing happened. I exited back to the main menu and tried entering the credentials that I tried creating and the game didn't recognize them. At that point I tried clicking Play as Guest and the game said I couldn't because I wasn't a "unit leader." I exited the game completed, re-opened it, and just hit Play as Guest and that worked to get me in. Still not registered, though.