Hi Ron - from your description, I cannot be sure if your issue is the same as discussed in this topic.
However, regarding the main issue discussed in this topic, yes - it has been fully understood. This appeared to be known Microsoft issue
related to using software VSS provider. One required step of Hyper-V backup process sometimes takes very long time with certain storage devices (for unknown storage-specific reasons), and when such operation takes longer than 60 seconds, it causes the STOP error (as explained in this article). Immediate workaround is to change HangRecoveryAction to 1.
Interestingly enough, this problematic operation never takes more than a few seconds in slowest test labs we have -- so, we could not reproduce this issue to date. However, one of the customers let us see and research this in his own environment, so this certainly helped to actually see the issue.
We cannot really speed up the storage reaction to Hyper-V commands since this is not something we can control, but we are looking at placing some workarounds from our side to reduce the chance of STOP errors happening. We hope that reducing the amount of CSV ownership transfer operations (which is when STOP happens) during the job by optimizing the VM processing order, as well as adding timeouts in a few places to reduce the load on storage should help with this.