I have an install that I get a flickering when I set the BR to upscale to 4K. The Sammy shows 3840 x 2160 while its flickering. When I set the output back to not to upscale and output to 1080p it works fine.
There is the possibility that the display "may" be bad. I and my helper both went through the menu and couldn't find anywhere to get the apps to load. At some point we were asked to download the You Tube app and it failed, it could have been from the browser. BTW, You Tube has some great 4K videos to see what a 4K can display. The last install we were able to use the ARC to get sound back to the AVR.
The equipment is:
Samsung 55" 8550
Yamaha RX-A1030 AVR
LG BP730 BR DVD, with 4K upscaling
Snap HDMI 7.5m cable, B6 (non active, I believe) going to the Samsung
Hopefully I have given enough info....TIA

dont let the BD upscale. the scaler in the tv is probably better.

Most likely the culprit is actually with the cable/distance.

with regard to the LG BP730 in particular, rule 1 is to make sure not to use the 'Auto' resolution setting. Note 2 is that even though it says it can upscale you shouldn't have it do the upscaling as it is questionable if the hdmi board is compatible (on a display by display plus cable/balun basis) so there can be some compatibility challenges, it should work fine for native '4k' streaming content though (when/where available).