Ethernet connectors shielding/ grounding
Unshielded installation: US style (your case 5, most professional equipment will have shielded jacks) - office Network
Shielded installation: EU style (your case 6)

unshielded or not/one sided connected shield... you can disturb the Ethernet easyly with near pulses, e.g. a power line with bad installed machinery next to a unshielded Ethernet is a problem. Just 1-2cm without shield or pigtailed connected shield (not an 360° connected shield) is enough to disturb the bus.
not connected shield or only one side connected shield are minimal better than unshielded in some cases.
shield connected at both ends does not cause any problem if done right (capacitive coupled with at least one resistor in parallel to get rid of static charge)! Industrial Ethernet - at least the European ones always use shielded equipment. Profinet for example defines additional meshed Points: connect shield every ~50cm or so to a Earth connected metal surface.
for industrial use, we select 360° shielded connectors, you can disturb the bus if you do not shield 360°. Standard is Variants of the M12 Connectors, which are good at vibrations also (RJ45 is not!)
The Profinet Guide on shielding and grounding...
https://profibus.com/index.php?eID=dumpFile&amp;t=f&amp;f=63888&amp;token=0f7b589224a95648a661b05a5ae08b71ff4652ea