There !may! be problem with SD/avi videos on 2.1.0 as it was with the previous ones. No users reported back so far if it works again or not.
New 12bit colorspace option on 2.1.0, also just may have some minor PQ benefit.
Otherwise: using PGS subtitles (converted with SubEdit) to get around the .srt subtitle issue, could be a solution.
KODI is unrelated, the best is to use HiMedia's own player. KODI has many other issues on this box with playback, not advised to use, only just for Browser/Library with the Wrapper (see FAQ).
KODI 17.6 works fine for Media Browser, but 18.x has an issue with External Player (Wrapper) handling, so not viable. Probably fixed in the final 18 release.