HEVC seek does not work properly on all files. Could be bad encoder but those same files seek correctly using Linux mpv and other players, so I am not sure if it is the files.
I find HEVC to be "good, but not perfect" and it does have glitches, but the driver is unfinished and is not upstream so that's to be expected. If other players work better they are probably using software decode because it's not possible to use hardware decode without a ton of patches right now.