I've got a RR 6.1.3 core with 3 agents; in the last 2 weeks (no hardware changes) I've noticed all of my snapshot and base image jobs are failing with the vague error "Failed on: Transferring"
The transfer will start and will transfer SOME data before failing.
I've rebooted my core and restarted the RR agent service, same results.
Agents are on the same LAN as the core.
what other troubleshooting steps can I take, or logs can I look at?
Look at the Apprecovry.log on the agent and Core.
If your clients are really taking more than 1 base image, as you mention. I would look to find out why (apprecovery log MAY help) Agents are supposed to only take 1 base image, ever. Of course agents will take new bases for a multitude of reasons, if it happens often, there is an issue you should address.
I had initiated the new base image to see if it would work when the snapshots were failing
It turned out the repository was full, which was causing the vague error message on backup. ONce I made some room in repository it started working again