I am trying to access a WMTS using this URL from ArcMap 10.3. I was able to get the list of layers (see picture below), and the service is shown in the Catalog Window.
Anyway, when I try to import it (by clicking and dragging a layer into the Table Of Contents), ArcMap always crashes. This seems not to happen with ArcGIS Pro and other GIS softwares (e.g. QGIS), while ArcMap 10.4 crashes as well. As far as I know, the WMTS I am trying to access is a static .xml file, which is not necessarily following the OGC standards. So the main problem could be some non-standardized lines in the xml, but this is just a guess, as I am not an expert of such services.
So I am asking if from the link I provided someone is able to understand what could be the reason of the problem (e.g. some non-standardized lines that show evident errors of interoperability), or at least if the problem occurs also on other machines other mine.
I eventually add that the Tile Matrix Sets shows two "subgroups" (see the picture):