I was getting the following error today when trying to send updates in the field today in Collector Classic on the iPad:

It's trying to write to a feature service that we have hosted on our ArcGIS for Server (10.4) and the iPad is 4G enabled. In one location I was getting about a 50% success rate in sending an update, and when it failed and I would get this error message. I moved to another location about 300 feet away and was just getting the update failed and error message every time.
I did some searching on the internet and here on GeoNet and haven't seen anything specifically reference this error. I'm at a loss as to what to try and troubleshoot to fix this. Has anyone seen this error or knows what is is referencing???