This would be unfortunate if this same intermittent error is occurring on iOS version of new Collector. Carl, could you provide more details to see if this is the same issue? A screenshot or exact verbiage would be nice along with circumstances when the error occurred.
We had two field crews that were plagued by this error this past field season (Android, current version of Collector, 18.0.3). I submitted a support ticket, but due to the intermittent nature of this issue, we didn't get anywhere. I've experienced the error personally once, but have not been able to recreate it. I've literally spent hours downloading offline maps, creating features, and removing the map in hopes of the error happening to me again. I wasn't entirely pleased with support's troubleshooting logic, so just closed the ticket. I asked for a version of Collector with logging enabled (something that is available on the current iOS version), but they thought it made more sense to recreate the feature service and use process of elimination to try and find what was causing the error. But since the error is so hard to recreate, I didn't think we were going to get anywhere with their approach.
I was hopeful that this would just disappear when Aurora for Android gets out of Beta, but now I'm a little worried with this latest news from Carl.
Ronald Vanderpool, did you make any changes? Just curious if there's a reason why you haven't seen it pop up lately.
Edit: One thing I should add is that the 'abort due to constraint violation' error is normally preceded by an 'unable to open file database' error.