I've enabled remote verification on my device, and I was able to submit sample data. However, each time my device attempts to send a periodic update to the Auditor service, I get the following error message:
java.security.GeneralSecurityException: device is not locked
I'm not sure what this error message is referring to. I assume that it refers to OEM unlocking, but OEM unlocking is not currently enabled on my device. I did enable OEM unlocking earlier, as I had considered either re-installing GrapheneOS or reverting back to Android, but in the end I ended up doing neither.