After several attempts, I left and was going to have someone else set up a table. I then saw that one off the tables I had tried to create/change in this way was in my list of games in progress. I went back to it, them I was finally able to change to normal mode, increase the number of players and invite my friends.

I can't guarantee that the table number I provided was one that initially failed.

I played solo, therefore I reduced the number of players to "from 1 to 1 player". That worked. But when I now try to play again, there is a message "You need to select a friend". When I do select a friend, there is a message "You need to increase the number of players at the table", but I can't reach the table. So I can't start the game solo, because the friend rule prevents it and I can't play with friends because the tables apparently are limited to one player. --> Deadlock, can't start the game any more :( .

Exactly the same problem as Vocmue

I have had the same issue as of today. The same as Vocmue and Triliem. I have made several attempts to change it, and have not been able to play since. I have been enjoying the game, and I am very sad and discouraged that I cannot play until this gets fixed. I also tried playing it on my phone as well, and am also having the exact same issue.

I had the same issue, set to solo but didn't play, when I tried to return to normal I kept getting error messages. I left the game and played a different game and when I went back to Trek it was fine. Didn't try F5.

just got premium today now i cant play any arena games due to this bug :(

Can't create any games in arena mode - it gives an error about solo mode only for Training mode.

Found a workaround: In the "Play Now" section selected "manual" Table selection. There I finally got access to my table settings and could change the number of players back to 1-8 and mode "Normal". After that I could go back and invite my friends without error message. :)
Dear programmers: Perhaps this has nothing to do with the game itself, but it seems, that there are some setting information cached, which are not overwritten even with the table setting dialog. Only going back to the place, where the settings are changed right before starting the game did the trick. Hopefully that helps finding the bug, good luck.