Hi Boyd, this is sounding like a suspend_data field issue to me, and it sounds likely that suspend_data is going over the 4096 limit, and therefore not bookmarking beyond slide 23.
Can you confirm that the settings are being maintained, for example the slide property to determine if the slide should Resume or Reset. This is usually the biggest culprit. If several slides are set to Resume, the data for data persistence goes into suspend_data and you can quickly run out. If not essential to resume a saved state of a slide, set to Reset to initial state.
I'm unsure why this would be so different from a 2016 file, as I've thought it was always a problem, unless your LMS allows more than 4096 characters, and Storyline is actively truncating suspend_data values over 4096 characters in later versions, and not leaving it to the LMS. I'm pretty sure Storyline has handled the truncating for a good while though.
Would recommend a test of both files on SCORM Cloud to see what happens with the 2016 file on there and see if it does exceed 4096 chars.
