A cable shield is basically a Faraday cage which needs to be completely enclosed and fully grounded on both ends. In a shielded cable with only one-end grounded, the ungrounded end is a high-impedance/maximum voltage-differential point, which causes the shield to capacitively couple any noise directly onto the twisted-pair Ethernet signal carrying wires. The shield stops being a faraday cage and instead becomes a monopole antenna.
I highly recommend you get a good book on the subject, such as → this.
Alternatively, pick your favourite AI Chatbot or even a Google search (which activates Gemini) with the following prompt;
Explain why HF shielding is degraded when a shielded Ethernet cable is grounded at one end only.
Don’t get me wrong, I have absolutely no problem with anyone experientially liking such cables (even if it’s usually caused by expectation bias). It’s when someone tries to justify/explain it with mistaken science that I feel the need to jump in 