Hi @vancej,
As a Canvas admin for higher-ed, I would suggest pushing back with Pearson tech support on this and ask them for more information on what they think could be wrong on the canvas side (I agree "unlocking" is not something on the Canvas side really). The ability to integrate learning tools with modern LMSes like Canvas is awesome, until you run into support issues like this. I've found myself in the middle of a vendor and Instructure pointing fingers at each other (or me) multiple times. If the integration is working for all but a handful of students, I'd recommend examining an account which does work vs one which doesn't work on the Canvas side to see if you can spot any obvious differences. Maybe there is a missing sis_id, or a non-standard character in the user's name... Aside from something like that, my experience is that these issues are usually on the publisher side. getting their support teams to realize this is very hit or miss though. Sometimes you just need to talk to a few different support people until you get one that's seen the issue and knows how to fix it on their side or escalate it to the right team to get addressed.
Hope this helps a little, even though it's not exactly a solution to your immediate issue.
-Chris
