There are rules. Do you have any of parts 9-16 in use of the performance you are coming from? Do you have any parts 9-16 in use of the performance you are transitioning to?

Things like ARPs and Motion Sequence can ruin your SSS experience since they do not tend to carry over through a performance switch (No trigger for ARPs when holding keys. Performance switching from doesn't get to "keep" it's ARP/Lane/etc settings, etc). So SSS is best used for "static" performances. I've argued before that performances which utilize ARPs and Motion Sequence should loose their "SSS" emblem since generally they change drastically when switching to a new performance.

... an aside:

To me, seamless means that if you have two preset performances with the "SSS" emblem - then when you hold notes and change from one "SSS" performance to another "SSS" performance - and record through the transition - hold the same notes and do not play anything more or anything less - that anyone listening to the recording couldn't tell you when you switched performances - because it sounds like nothing changed. Anything outside of this experience would be considered having a seam. Plenty of "SSS" emblem performances have such a seam. I am making a marketing argument - not a technical one. I do understand the issue is a lack of redundant registers for all aspects (like ARPs, Lanes, etc) which would otherwise provide a true seamless experience. I just don't see the "but" in the "SSS" marketing - or an asterisk next to "SSS". I do think it's misleading to have "SSS" on performances that so drastically change through a transition and would rather have them better labeled. I can double check - but I'm not sure any presets (except an init one) has SSS removed. If "everything" shows "SSS" then the emblem loses any meaning or usefulness. My proposal would at least let the emblem carry some useful differentiation.

Some past discussions:

https://www.yamahasynth.com/forum/sss-seamless-sound-switching-might-be-the-way-it-works-but-wish-for-a-fix
https://yamahasynth.com/forum/sss

BTW: using google to search for "site:yamahasynth.com SSS" finds previous posts covering this topic.

Jason you Legend. Thank you very much for your detailed explanation.

For some reason I had 2 parts in 9 and 10 which I've deleted and the SSS works.

I've also read your other threads to understand this better.

I love the Montage and every day there's a new discovery ‼️

Glad you were able to identify the culprit and also benefit from some previous forum discussion surrounding this feature. Due to Montage's generous PART/element allocation in a single performance - I do not use SSS as much as I would otherwise if more limited within a single performance. Generally, I combine what previously would have been several performances into a single one. I'm sure in the future (future product most likely) "SSS" will have no disclaimers and will be as fast/instantaneous as switching between PARTs within a single performance and also allow for ARPs and any other automated performance features (today motion sequence - in the future ??) to carry through switching from one performance to another. When that day comes, I will likely use SSS instead of in-performance-switching because it is helpful to have the song name. Currently, when I switch scenes - the name does not change so it's hard to remember how I've allocated my scenes once my setlist gets large.

This is a tangent - but it would be nice to allow each scene to store a text label for what that scene is for. Then when switching scenes - the scene text is displayed instead of the performance name (or scene name is in a big font on the screen with the performance name in a smaller font below) . This would allow for better documentation during the set and may allow for some to place say a short chord progression in the scene text or other performance notes for a given section.

I know text storage takes up lots of room and particularly if you allow MIDI address space to access. I would prefer no MIDI address access and instead require a USB stick with the descriptor file (such as SCENES.XML) which can be edited as a text file. XML only as a suggestion to make parsing associating scenes with performance names easy for Montage - but any format will do. Maybe the old windows ini file format:

[My Performance name]
Scene1=Happy Birthday (org)
Scene2=Old Devil Moon (p/b)
Scene3=Country Tune (v/ps)

[Another Performance Name]
Scene1=A:CM7 D7b5 D-7/G7 CM
Scene2=B:FM7 // D7 D-7/G7

Still assuming text fields are limited to 20 chars (so above limits to 20 chars - which is why "CM" at the end of Scene1=A:... is missing the "7". Ran out of characters.)

Montage would look at the SCENE.INI or SCENE.XML file and "load up" the values from USB instead of having to consume internal resources. Performance switch times would be slightly delayed for things like SSS to load the settings from a file - but user would decide if providing the file is worth the extra delay or not. Obviously if Montage has tons of internal storage left for scene descriptions - then using internal memory would be fine - but assuming resources are more limited.