Per my support case (645364) I have recently found out that my config diff emails seeming to be poller-bound is actually the expected functionality of NCM. Before an upgrade to NCM 7.3, one config diff email job contained config diffs from all licensed NCM nodes. Now, a scheduled diff email contains only diffs of configs for nodes on one poller or the other.
I haven't come up with any workarounds yet to send one email with all config diffs. Contemplating no longer sending config diff emails as I don't want an unseen config change (not looking at the right email) coming back to haunt me. I most likely will stop config diff emails and get end users to use config diff page I created.
For those of you in multi-poller environments, do you send config diff emails? Did you duplicate your primary poller's job to your additional poller?