Of course there are different differences.
What I recommend? Live with the issue until there will be time to fix it. And you already open an issue here on forum.
In fact @vpeter, I’ve been dealing with this problem for a few years now. And considering that CoreElec has, in my opinion, reached a very high level of functionality and compatibility, I thought it was a good time to talk about it. But I will continue to wait as long as it takes. It’s not so bad. 
1 Like
@MoojMidge, in order to update and centralize all the data collected during this research, can you confirm or deny my understanding of the hypothesis you exposed.
Your hypothesis is that Kodi CoreELEC looks for the keyframe after the chapter marker when browsing. Which could cause a delay because the player has to decode the entire sequence of images up to the chapter point. While Kodi (anothers Platforms) looks for the keyframe before the chapter marker, which allows for faster synchronization.
Is it this difference that you think could cause navigation problems between chapters on CE ?
I also take this opportunity to share the recent response from CrystaIP, a Kodi developer :
" I was able to download the sample finally, and with or without hardware acceleration, no glitch. with remote, with OSD buttons, through bookmark/chapters, … (Windows on desktop PC).
Hardware decoding is still the likely culprit, but it cannot be clearly confirmed with that video on your device because it’s not powerful enough to decode it without hardware assistance. Find another lighter video that still shows the issue with hardware decoding and is smooth with software decoding. You may have to go down to H264 codec and 1080p or lower, or even further down to mpeg/xvid and dvd resolution. It depends on the strength of your CPU. Then test the chapter jumping with hardware decoding off. "
Please try chapter seek with tomorrow nightly, CE-21 20240425, again.
There was a patch from early CoreELEC days still applied to Kodi.
This patch was need in past because the seek did might not end up on a keyframe.
So it did a step forward to the next keyframe. This cause like in this example a diff of 10 seconds between chapter position and keyframe position. And this did lead to a lock out in the chapter seek function.
I guess Kodi seek does now end up on keyframe since a while ago so this extra seek is not need anymore.
1 Like
I just made a build of my own and stuck chapter issue seems to be fixed. I can go back now.
But the issue of skipping an extra chapter still exists. I can consistently do it when there are only a few minutes remaining before the next chapter. For example, when it’s used to skip an intro in a TV series. Eg. South Park.
I can provide a sample from Star Trek TNG for this.
1 Like
Thank you very much for your interest Portisch. For my part, after testing several problematic films, the chapter passage bug is resolved. This is really good news. However, I still have the problem of thumbnails not displaying. And when you click on it, the movie currently playing stops immediately.
What we can see at the 25th second : https://youtube.com/watch?v=LLptQ5pNKrY
1 Like
Please always compare to nightly Kodi Windows, Ubuntu Linux or Android if it’s same.
1 Like
Are you playing from same source? Can you try to play some local file on CE device?
1 Like
Yes Vpeter, the source is the same for all platforms, it is a NAS. In these conditions, it works perfectly on Android, it’s very responsive. But it doesn’t work at all on CE under the same conditions.
However, if I store this movie on the device’s internal memory, then the thumbnails work on CE too.
How can I give you the link for the sample? It’s a 10 minute sample from Star Trek to check for chapter skipping.
This video shows the issue clearly, when the video is close to chapter mark it skips two chapters.
I tested on LE generic and on Windows and there it behaves the same for. Local files shows thumbnails but remote over HTTP doesn’t.
1 Like
Why would this work on Android, but not on Windows and CE ? (I configured SMB network for Kodi Android and Kodi CE)
Use Mega.nz
False joy ! Strange phenomenon, it worked for a few dozen minutes on films that usually don’t work. The chapter thumbnails worked perfectly. And then some time later, the bug returned. 
After discussing with content creators, UTF8 chapters with names with special characters (accents, etc.) may not be supported. What do you think ? Would Kodi Android benefit from better compatibility than CoreElec with reading chapters ?
Upload a sample. Should we always be guessing things like this…
The sample I shared in my first post is still valid…?
On CE it works exactly the same for me as on Windows. So try on Windows yourself.
1 Like
I carried out numerous tests, which allowed me to notice a strange thing. By launching the video directly from the file browser rather than from the media library, it works well. The thumbnails appear well and allow you to navigate the film from one chapter to another. But the big problem is that going through this, the video takes 2min20 to start.
Then I tried to recreate the chapters myself with and without special characters, but in all cases I ran into the same problem. So special characters are not the cause of the problem.
What could possibly be causing this problem? And why does it work perfectly on Android and not Windows? Mystery.
I will update my first post with all this new data. I have reached the end of my skills, so for the future, I can only rely on you.