In previous versions of Moodle (e.g. 3.1.3), we were able to launch AICC HACP courses inside Moodle, which were sitting on an external domain, and these courses would store information in suspend_data.
Nearly 100 pieces of content have run like this for over 12 months, with our clients using Moodle and Totara (also Unicorn, Kallidus and other LMS's) to configure and launch them on their own LMS instances. These instances have been tracking correctly, recording session time, score, lesson_status, lesson_location and suspend_data.
In our particular case, suspend _data is used to track previous progress information, which is used to populate the content (i.e. with previous question responses) if it is opened again at a later date.
Approximately 2 months ago we started getting reports that some clients were seeing the courses open and lesson_location, session time and score were being recorded but suspend_data was empty after the course was closed.
We have replicated this issue and we can see suspend_data is NOT stored for AICC HACP (external link) courses in Moodle 3.4.1, 3.5.2 and 3.5.2+.
We can see that it does work in and is stored in Moodle versions 3.1.3 and 3.2.
To be absolutely clear - the same course works in these Moodle versions if you upload it as a SCORM 1.2 package. Suspend_data is stored in this case. The issue only occurs if you run the course by configuring it using an AICC external link.
If it helps, I can provide an external AICC courses link to anyone trying to replicate this issue but I will need your domain name as access to these courses is whitelisted in our course repository.