This might not be exactly the right forum to ask in, as it is a bug with the website itself rather than with battle mechanics - but I can't find anywhere else to report it.
Sometimes when I select a format (particularly just after I open the website) on mobile, the format does not change properly. By this I mean, the text that says which format I am playing does change but the team I am using stays the same as the old format.
Then, when I try to play the format it tells me that I have to select a team but, because it's still on "random team" I can't?
Another way this happened was it let me have a team selected going into a random battle - then when I tried to start the battle it told me that I wasn't allowed to have a team selected (unsurprisingly) and to report the bug, which is what I'm doing.
View attachment 499211