I’ve just had a similar problem with Metz connectors on a new Wireworld Chroma CAT8 ethernet cable. The connectors do seem to work okay in a brief test in the ethernet port of my Roon Nucleus, but these Wireworld connectors would not hold a connection at all in a pair of cheap TP-Link TL-SG1005D switches that I have been using as place holders until a planned switch upgrade later this year. I contacted Wireworld tech support; they suggested that the problem might entirely be with some design problem of the TP-Link switches—even though those switches work perfectly for me, without any connection problems whatsoever, with every other non-Wireworld cable I have on hand, from cheap CAT 5 to Blue Jeans CAT6 to Audioquest Cinnamon and Vodka cables.
When I went ahead and blew some more cash on a pair of brand-new Cisco SG110D switches, the connection with the Wireworld Metz connectors worked much better, so perhaps the ports on the TP-Link switches hadn’t had the best design. That said, at least one of the Wireworld Metz connectors is clearly still more loose in the Cisco switch than any of my other cable brands; I can interrupt the connection by moving the cable with my hand, and I’ve had one spontaneous dropout so far, which has never happened to me ever with any other cable, even with the cheap TP-Link switches.