Hi Sam,
I am also experiencing similar sync-fail difficulties with an AGOL-to-Enterprise Distributed Collaboration. I have not resolved the main non-sync issue, though I have been able to clear at least one of the reoccurring log error items by unsharing, then resharing the layers in question. Also, it may be worth checking to see if any of the files have 'Delete Protection' turned on. Apparently, this can block them from getting overwritten in the receiving portal--in the case of layers and views being sent as 'Copies'--and this setting seems to be passed along with feature layers from the originating Portal, so start by checking there.
Also, one disconcerting blurb I came across in the documentation is that it doesn't matter so much what version of Enterprise you are currently using, so much as what version you were using when you first created your collaboration: So, if you've upgraded your Enterprise since creating your collaboration (as in my case), you may unknowingly be bound to the limitations of your previous version. I only mention this as you are using 2-way editing which is a more recent capability.
Anyway, I've opened up a ticket as well, and will be keeping an eye on this post to see if you are able to resolve the issue.
Good luck,
Greg