[nhsman]

So you are saying that software deinterlacing works as it supposed to? Maybe when I watch it on the big screen the impression is different. However none of the settings on Kodi 18 makes the deinterlaced and scalled video comparable to the same video played on Kodi 16 on the same display, quality wise. How comes?

BTW.  How about VAAPI deinterlacing, is it also working on your system?

 I am not saying that there is no issue but I doubt that there is one related to ffmpeg's deinterlacing method. Deinterlacing artefacts are very noticeable and I don't see those with sw decoding and deinterlace. You said that sw decoding with deinterlace does not work at all. I can't confirm this. Can you check this again? 

Just double checked that and in deed sw decoding and 'deinterlacing' work but in my case the picture is not as good as in your screenshot.