I got this error as well and found a super weird fix if you're using sideloadly. If you try changing the app version to 1.13.3, some reason the game becomes a black screen after importing your account so instead, you change the app version to 1.13.4. I've put the steps below as well
Delete app completely from device
Change app version to 1.13.4
Install app onto device
Open app
Load account (will force the app to quit)
Close app and close it out of the multi window switcher so it is completely closed
Open app
Should be able to play on your main account again
Edit: I started getting this error because I wanted to try purchasing the $10 IAP to get the sweep option. I had to use a second device to use the non hacked version of the app, load my account, make the purchase, and then got the error. After doing the steps above I could play again and the sweep to spam click one spot for diamonds is extremely OP and crazy fast compared to manually fighting through dungeons.