Under investigation. Occurs very infrequently, making reproduction of the issue (very) challenging.
Seems to occur with older Paths only / in particular.
Previously applied fixes seemed effective, but the issue somehow re-appeared, anyway, after a while.
How to fix / Workaround
1. Disable the option that forces users to complete the Milestones & Steps within a Path, in order
a. Go to 'Manage Paths'
b. Open the Path, or select 'Settings' and then 'Edit'
c. Click the 'Content' tab
d. Make sure the Path property 'Participant must complete Steps in order' (at the top) is unchecked.
2. Create a new Path and re-embed the video. Optionally, you can copy an existing Path ('Manage Paths', 'Settings', 'Copy Path') in order to make this easier.