Slow speeds on both 2.4 & 5 ghz. Model EX6200/AC1200

[Kodakguy]

I'm experiencing slow connection speeds with my 3 year old EX6200 range extender. It's kind of always been the case, but recently it's gotten really slow. Lots of buffering and frozen screens. Firmware is current. All displays, 2.4ghz, 5.0ghz and the communication indicators are all green. The extender is attempting to grab a signal from 1 or 2 of 3 directional antennas that are connected to the resort owners modem that's about 170 feet away. The extender is line of site to the directional antennas but has to look thru a glass sliding patio door. And actually, the 3 directional antenna are new within the last week and are closer than the prior 1 directional antenna that's been up that last 3 years or so. Have I been expecting too much from the extender? Can I attach my own directional antenna to the extender somehow? Thanks to all who reply.