Works for me, thanks!!!
I've been struggling with this problem since late January or early February.
Most of the solutions proposed worked, but only the first time.
I installed the game on Android, and in more than 3 months I never had any problems. Also, playing on a Windows 10 PC without updates up to date, I have no problems either.
I thought maybe it would be a random problem, but no. I think the error depends on which server the game connects to. How do I find out? Because of the advertisements that appear before playing.
Whenever I see advertisements of this style (even if they are different games) the progress is not saved.

And whenever these types of ads appear, the progress is saved correctly.

I tested this hypothesis for more than 2 months, and it always happened as expected.
Also, if I started the game, the GOOD ads appeared, played several challenges, then for a matter of time the ads appeared again, but in this case the BAD ones, played more challenges, then closed the game, and when I came back, only the progress up to the BAD ads had been saved. .