I bought a 2018 Q7FN about a week ago because I found it new on clearance. Worked fine for 5 days or so then displayed the OneConnect cable issue screen while playing PS4 last night. TV started rebooting repeatedly, about every 10 seconds. Tried unplugging TV for a long time, won't stay on long enough for Reset, remote control unresponsive so cannot enter Reset code. Tried reinstalling One Connect cable with no success. Super disappointed! After reading a lot of the posts about One Connect box/cable problems, I'm skeptical if waiting for a replacement is even worth it.
I talked to Samsung on the phone. They thought it was a one connect cable, quoted 7-10 days to ship it. The store I bought it from was only 30 day return and that was cutting it really close so I just returned the TV. From reading the reviews, it seems like a faulty one connect cable (or box) is a common problem even on brand new sets. Not sure if this feature is ready for prime time.