Mine is going back, the green screen actually looked pretty terrible last night. Curiously I checked for this at the weekend and it was not there at all so feedback that this is phenomenon that appears and worsens over time seems to hold true.
Currys had no replacements to offer me so they are refunding it. Think I may just pick up a Note 9 and scratch that Note itch, it’s either that or the OP6T but there are a few too many compromises on that for me right now (no wireless charging, no always on display) The Note looks interesting and I have never had one so it should be fun!