With the game in safe mode, or with mods uninstalled - his frame rate went right back up to normal (170+). I worked with him on re-installed the mods, and it ran fine initially. He then made config changes, and tripped the issue again. He re-installed the mods again, and is fine with the current config. I'll suggest he capture logs if he sees the problem again, as without them (logs to review) - it's trial and error on his part. Appreciate the advice!