Updating a multi-instance user defined table (GET and PUT request REST API) created through Panel Editor not iMIS Desktop

I have a client who's REST API calls where working in iMIS Version 20.2.46. Now they have upgraded to iMIS 2017 SP M and the previous API calls are just not working anymore.
i.e. GET request from multi-instance user defined table
https://{url}/Asi.Scheduler_iMIS/api/StudentGrades/20303,2 used to work
Now only https://{url}/Asi.Scheduler_iMIS/api/StudentGrades?ContactKey=2015287&Ordinal=2 returns this one unique record.

The PUT request used to work now it simple states 405
{
"$type": "System.Web.Http.HttpError, System.Web.Http",
"Message": "The requested resource does not support http method 'PUT'."
}

What am I missing here?
Any pointer is much appreciated.
Thanks much,
Alex