Most of 4K60 HDR videos are encoded without MaxFALL/MaxCLL metadata. Also HLG DVB streams don't use HDR metadata by design. Current HDR implementation in Kodi checks for the presence of metadata and if there is none or if it is "incomplete" - HDR passthrough is disabled. IMO this behaviour is incorrect, so I PR'ed this fix.
I really hope this gets put into master soon. All my HDR files switch my tv into HDR mode on Kodi on android, unfortunately most of them don't on Libreelec.