That’s odd, looking the log I see the warning “No enabled versions found for service WMTS, falling back to highest supported version” which is strange and indicates it intends to negotiate and return 1.0.0 - The only question in my mind is does WMTS support version negotiation in the spec? and are there any other versions available?
From a quick look at the code it looks like GeoServer expects GWC to handle the version negotiation but this doesn’t seem to be going down that branch and for some reason the code is not finding a version.
I’ll raise a ticket but I’m not sure when anyone will get a chance to look at it