iPhone sync to Groupwise Not always Consistent

I have one of our owners telling me that his new iPhone (iPhone 7, iOS 10.2, protocol 14.1) does not always send things to his Groupwise account. He can see two calendar items on his iPhone that are not showing on his Groupwise calendar when he view it. He wants to know if there are any issues with it syncing from the iPhone to Groupwise. I said I didn't think so. It seems that the other items show up in both places. I checked the synced status in GMS and for calendar items, it shows 0 pending. I am assuming that is for from Groupwise to the device? There is likely no way for me to know what's pending on his phone......

Could just be a fluke? Is there any issue with an item having been entered on the iPhone7 first then syncing to Groupwise?

Is there any way to force the iPhone to resync in that account?

Kind regards,