Time Machine / Backup issue on 2016 MacBook Pro

Spoke with Apple Support who elevated my call to another agent. They have requested engineers to look into issue which takes a few days. Also, as a follow up, I mounted my two external drives to my 2013 MB Pro and there are no issues in copying files from one drive to another. So, it's either the adaptors that are the problem or the 2016 computer hardware...

There are two know issues with Adapters:

Note: The Apple USB-C Digital AV Multiport Adapter is not compatible with the G-Tech G-DRIVE mobile USB 3.0 Hard Drive (Apple part number HF4F2VC/A).

and the 'default' charge cable is not really a ThunderBolt cable at all:

This charge cable — with USB-C connectors on both ends — is ideal for charging USB-C devices, and also supports USB 2 for syncing and data transfer between USB-C devices [at USB-2 speeds maximum].

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For clarification, in my case, I am using two G Tech G Drives (4TB, Thunderbolt cables that come with drives) and also using the USB-C adaptors to connect those drives to my new 2016 MBPro. My separate G Tech external drive (for Time Machine only) using USB-C cables that come with unit gives me no problem when backing up using Time Machine. Of course, I am not using adaptors in this case.

I performed some data capture procedures per Apple Engineers requests for them to investigate. No remedies as of yet. However, I read on Mac Rumors that the new Sierra update (soon to be released) apparently fixes many of the problems involving external disks. The article appeared late Wednesday or Thursday so check it out.

I have been using an airport time machine with no issues. After reading this post I was curious and decided to try a connected backup on my 2016 MacBook 15". I used the same adapter Apple USB C to a Samsung 240GB EVO SSD SATA III in a Sabrent external HD enclosure with a USB 3.0 connection. It worked flawlessly. I know it doesn't help with an answer to your problem but may help with diagnostics. Whats different?

I have exactly the same issue, with about 550GB to backup from scratch.

The buzz on the web is that Sierra update 10.12.2 (expected real soon now ) contains a fix. I intend to cross fingers and wait. I also seem to be able to avoid crashes if I stop the backup after about 10GB and then immediately restart it - it's going to take a long time!