Hi lenigma,
I am Sumit, an Independent Advisor and a 2-Year Windows Insider MVP here to help.
There is not much documentation about this provided by Microsoft. As a first step, disable Windows Sandbox, restart, and try enabling again. Technically, each instance of Windows Sandbox is a fresh start so there should be no cache which you can clear :)
https://www.tenforums.com/tutorials/123777-enab...
Content on the above blog is written by a Microsoft MVP so it is safe. However, do watch out for the ads.