Yes, you go back to the LMS provider, point out that it works perfectly on SCORM Cloud and other Learning Management Systems and explain that the reason it doesn't on their LMS is because their code is changing double quotes in the suspend_data to HTML entities (why on earth?!) - then ask them to please stop doing that as well as any other forms of modification to the data in suspend_data.
Interesting that the course is throwing a 'could not connect to LMS error', that's a bit misleading. Will see if I can fix that.