joining two or more splits causes skipping and frame corruption
I started with splitting a tv show ep into parts (5 total) intended to be kept using split "by parts based on timestamp", discarding the scene I don't want. The show is in HEVC 10bit by x265 and AAC audio. The timecodes are obtained from mkvinfo and each part starts with an I-frame and ends with the P or B frame prior an I-frame (scene change). All parts play well individually, from start to end, and even mkvinfo outputs the same adler for each part, original file and final joined file and no differences in frames (added or missing) have been seen in the output, and by this I mean the frame that ends a split and the I-frame that starts the next split are next to each other in the joined file, same adlers.
Again, the parts play fine individually, but the final joined file has issues only on some "joints". It plays fine where split 1 goes into 2, 2 into 3 and 3 into 4, but 4 into 5 it introduces skipped frames (2 or 3 sec), artifacts after that, on the initial sequence of part 5 (as if it doesn't start from a I-frame, but mkvinfo shows it does), and then it plays correctly, presuming it encounters the next I-frame.
I've tried --append-mode track when joining the parts, same issue. I've tried playing it in MPCHC+LAV and VLC, same issue. I've tried joining just part 4 and 5, same issue. Issue appears when playing the file in one go. If I use the controls of MPCHC to go back to that keyframe starting part 5 in the joined file, it plays fine. Same for VLC, although it doesn't allow jump to keyframe so I've let it play and guessed when to jump back, but the parts in the images attached played fine as well.
I can't figure out why part 5 gets showed that way in the joined files when played in one go.
I've also mkvinfo'ed all 3 files, joined the results of the two parts and compared with the joined file result and the compare utility (bcomp) shoes the only differences being the timestamps of part 5 vs the joined file, other than that, frame types and order, checksums, frame sizes are a perfect match.