"This is rare, but the Smart Campaign experienced an unexpected hiccup and some flow steps may not have succeeded."
Until recently, I think I had only received one or two of these errors, if any, in 1.5 years of using Marketo. As of March 16th, 2019, I've received 26 of them. They're all related to the same smart campaign that I use to process Lead Source / Person Source, and they loosely coincide with a change I made to make the Smart Campaign flow steps more granular, but I can't trace back my steps to figure out what could have gone wrong.
The smart campaign is relatively simple yet detailed:
There are 24 different "choices" for the CDV for Person Source, and 31 for the Sub Lead Source field. Any ideas about what could be happening?