I also notice that browser GET request to something like https://nuget.abp.io/76eb528e-8c3c-4379-9b6d-b5e7a6451e9e/v3/package/volo.abp.auditlogging.domain/index.json results in the same error 500 (I used some random GUID)... However, if I do same request with our real GUID value, it result in status 302 and redirect to https://nuget.abp.io/Error?httpStatusCode=404 page. So even from browser I can't make it work now with both real GUID and fake one...
I can't tell exact times because I don't see that info in Github Actions executions... It happens 10 March 2021 and before, at least few times per day. Today we temporary fixed that issue by including NuGet packages folder in our Git repo, so restore process don't try to load them again from your APIs... So if you can just take a look into requests which error 500 on 10 March 2021 to something like https://nuget.abp.io/OUR-GUID-HERE/v3/package/volo.abp.leptontheme.management.application/index.json you will see it's our requests.... (let me know if I need to provide you our value for OUR-GUID-HERE)