outdoor rated cat 6 FTP cable not connecting at 1Gbps too long? (50m)

I have using a 50m cat 6 FTP shielded cable to connect downstairs with upstairs. The cable is run outdoor for convenience... problem is the cable does not connect at 1Gbps but at 100Mbps instead... :(

I thought it was electrical interference or other cables (etheet, coaxial cable) .. so I made sure to isolate the cable from the other cables for testing but I still can't connect to 1Gbps.

I tested my switch and router to make sure it is gigabit and it is.

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