Thanks for your reply.
Our app targets "netstandard2.0" and is deployed on Azure App Service.
Cert is created like this:
Certificate is cached for 60minutes using C# ObjectCache.
This cert is then used to acquireToken like this:
await context.AcquireTokenAsync(audience, certCred, sendX5c: true);
The issue is: acquireTokenAsync throws the exception "Keyset does not exist".
This issue happens every few months and is not easy to replicate. Sometimes it would go away by itself and sometimes we'd need to change the app service plan and that will fix it.
Any pointers/suggestions would be extremely helpful!