DCC2 - 2100 only using one GPU on multi GPU systems

[bkuzma]

Interesting oddity here. I have multiple password cracking boxes, and I've noticed that DCC2 type hashes will only use one GPU. This is the case on two different four GPU systems, and a two GPU system. This issue cropped up running Hashcat 6.1.1 on Ubuntu 18.04 LTS, but I've also observed it on 6.0.0 and 5.1.0. 

Other hashtypes (specifically 1000 - NTLM and 7300 IPMI2) are happily using all the available GPUs. 

Has anyone else observed this behavior, or can you suggest some troubleshooting steps for me to look at? 

Thanks!