Hard to diagnose these types of issues on the forum. I recommend if you're using a paid version of the product that you open a support case using the Tools - Diagnostic toolbar option and the Support team can review the logs. If you're using the free version, then I'll reply back if Support has an answer for you on this issue. I do know one customer who reported something similar was able to restore on a second execution of the restore. SO you may want to try that.

We deprecated many of the cloud vendors what were not being used by our customers. I'f you lookng for low, long-term archival storage tier pricing, then your will find many options from AWS, Azure, and Google Cloud. Also consider Wasabi or Backblaze B2 for low cost, hot storage.