I just tried it with a position from a game I lost and it worked well.
But that doesn't fix your problem. I don't think it has anything to do with your having a non-Premium account.
You should use the bug reporting tool on the Support site to let them know. If other people have the same problem, they may be able to diagnose it.
Thank you for the report and suggestion about the bug reporting tool.
I tried on the phone app and it works there. But, I tried some more using a different Google account I have, same bug. I even tried using Windows 10 instead of my usual OS (Fedora Linux) and same issue. I don't have any ad blockers running. I'll try and pursue it some more with support if it doesn't get fixed soon. I have no idea why it would just be me; especially when I tried a 2nd account and had the same issue. Maybe its only a Google account login thing, no idea and I've done enough debugging for now.
I've got a free account.
Up until a few days ago I've been able to create a custom position in the analysis section and then practice vs computer or analyze a past game and practice vs. computer from a position in it.
I've tried multiple browsers but now whenever I select practice vs. computer it opens a new tab on my browser and loads the position like it should but it will never move a piece. It just sits there with 3 dots flashing in sequence like its thinking forever. If I play from a position where its my turn to move it will let me move but then again it will just sit there flashing the thinking dots forever and never move.
Anybody else having this problem? I've used these features many many times over the last couple months but now its broken for me and I really miss it.
Perhaps its because I have a free account and theyve disabled that feature? If so, it should tell me instead of just acting all weird.
Its a great feature for example if you want to set up and practice an end game where the only 3 pieces left on the board are the 2 kings and your rook.