[noggin]

Thanks, knew it wouldn't. Wondering how best to re-encode .

4:2:2 is the issue - though the Raspberry Pi 4B may cope with it (unusually the Pi 4B has a 4:4:4 capable HEVC decode engine I believe - so should support 4:2:2). Everything else will need a transcode to a 4:2:0 format.  If you have an Intel machine that's relatively recent knocking around then Quicksync HEVC encoding is pretty fast in ffmpeg.  I re-encoded some very high bitrate (440Mbs or higher) HLG ProRes 2160p25 4:2:2 stuff to a format that played fine on consumer 4:2:0 gear.  I usually run at a constant quality - and run 4:2:0 HEVC 10-bit as my output - even for SDR content if the source files are 10-bit.

However I'd give the 1080i stuff you have re-encoded with decomb a decode with -filter v "w3fdif=complex:all" as you may see that deliver nice full 50Hz motion with few motion artefacts. (It's a clever BBC-designed V/T - vertical/temporal filter that isn't adaptive and doesn't try to track or detect motion.  It was the standard deinterlacer used in lots of broadcast hardware for many years)  Personally I prefer Weston 3-field to YADIF 2x on most content - though fast 80s electronic rolling credits can sometimes defeat it.