@MR.S I missed that you have already tested with a short cable. sorry :-) how long is the cable from the switch to the access point?

@guyd2 if the port is disconnected after you set 1000Mbps, there is a fault with the cable or the access point. try connecting the access point directly to the switch with a short patch cable. if you...

@StephaneDupont have you tried turning off Unscheduled Automatic Power Save Delivery. is this the symbol of your clients having problems?

@guyd2 goto port configuration on the switch

@KuroPhoenix https://www.tp-link.com/en/support/download/tl-sx3016f/#Firmware

@LincolnMcCurry you set power saver on the access point properties, config and advanced