To resolve this please try the following
1. Make sure
Trados Studio ( including any error message) is closed
2. Go to
C:\Users\%username%\AppData\Roaming\SDL Community\AppStore Integration\Settings (just paste the path in Windows File Explorer and hit Enter)
3. Rename the
settings.json file there ( to
settings_old.json for example)
4. Start
Trados Studio and check if the issue still occurs
Optionally you can set up the private app store again following the same steps in the thread below and make sure there is no whitespace at the end of the URL ( https://studio-appstore-api-trial.azurewebsites.net/)
https://community.rws.com/product-groups/trados-portfolio/rws-appstore/w/wiki/6403/private-appstore 