OK, after a bit of research I think I may have solved the problem.

I gave the survey company the code: surveys.mcgill.ca/limesurvey/index.php?s...=xxxxxxxxx&newtest=Y

and set the outgoing URL to www.opinionshere.com/surveycompletion.as...S:47539X10468X419346 }

I took all the URL-related code out of the hidden question and left just the line hiding it.

Hmmm, I don't know how the questions are referenced in 1.92, and I guess most people here won't have a 1.92 version installed to be able to help yu in detail. And I am also no Javascript expert. Sorry.

I would:
1) Create a hidden equation type question with qcode "OTXID"
2) Prefiill this question with the provide id (contained in the url). If using tokens it's easier to use a custom token attribute
3) Pass the value in the end url/redirection using {OTXID} :
.../surveycompletion.as...&otxid={OTXID}

Note that 1.92 version is the 1st LS released with Expression Manager (EM) engine...so you can minimize the use of exact IDs for surveys, groups or questions

For example you can hide a question, pasting in the help area of this question:

CGPsurvey2016 wrote: OK, after a bit of research I think I may have solved the problem.
I took all the URL-related code out of the hidden question and left just the line hiding it.

Yepp, correct way to do it. In the old day this was the way to go.
Wasn't hiding questions via advanced settings already available? I never used any javascript code to do panel integration.
The panel staff was often confused by the crazy GET parameters (12345&47539X10468X419346=) Limesurvey needed .

When using panels I never allow to hit the exit and clear button. Limesurvey allow no easy way to redirect to a correct panel URL.
After hitting that exit button the panel link has to be clicked by the proband which isn't bulletproof. Since
the "Answers cleared" screen also provides links for "Restart this survey" and "Close this window"