I tried to reproduce your issue with the project filters, but everything worked fine for me.
Basically you will have to add the name of the project in the input field and that is all. The warnings/errors from the project will be muted.
Once you have added the project to the filter do you find any problems reported in JustCode's error
You can open it from VS JustCode menu > Windows > Show Error List window.
In order to investigate your case further I will need some additional information like project names and the string you input in the filter field.
Also, the logs from %localappdata%\JustCode\Logs folder might be useful so consider sending them in a private ticket.
For further guidance I will suggest visiting our help article
which provides explanation for the patterns available for the file filter feature.
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