Same here. I have a Netgear Nighthawk 7000 router, and a Netgear EX6250 extender. My Roku Streaming Stick+ has been working fine since I bought it back in Jan. I added the EX6250 to my network after setting up the Roku, so the Roku was setup against the Nighthawk. The EX6250 has always been closer to the Roku than the Nighthawk but I never bothered to see which AP the Roku was actually connected to.
On Saturday, I moved my router to a different room further away from the Roku, and now it won't connect to wifi. In fact, it behaves very badly - freezing and stuttering in the main menu, so it's essentially unusable. I managed to factory reset it, and now I'm stuck connecting it to a wifi network. It shows full strength for my network but won't connect to it. I assume the problem is that my Nighthawk router is too far away, so the Roku is trying to connect via the EX6250.
There are many other threads like this in the forum, where folks can't get their Roku to connect to the extended AP of a wifi network.