Hi @Eric_Hemmerlin and welcome to MongoDB community forums!!
The error message in the log you posted seem to indicate that the backup is corrupt, or the hardware is corrupt.
Could you share a few details of the hardware on which the cluster is deployed like CPU, RAM, core, free space etc.
However, since the cluster is deployed using different technologies mentioned, one of it could also be the possible reason of the failure.
The suggestion here would be to debug at each stack and let us know if the issues are specific to MongoDB?
Note that if the underlying issue was caused by incomplete backup or corrupt hardware, there’s not much a database can do to overcome them.
It seems to me like you are backing up all three nodes separately. Is this correct? Note that for a MongoDB replica set, typically you only need to backup one node, since the set contains identical data. You can restore this data to three nodes as per the restoring replica set documentation
Regards
Aasawari