We are trying to connect activities from an external LTI-provider with a moodle course. Grades are supposed to be synched. The LTI-provider showed us a moodle class of thei own in a 3.4 Moodle with grade synch working.
They could not achieve to get synch working in our demo Moodle 3.2.2+, we ourselves tried everything we could think of as well. I also checked the server-timestamp - it is not off.
A student completes an LTI-lesson, he is recognized with his name given by Moodle there, his points are shown in the lesson, but not synched back to Moodle. Also there is no structure in the gradebook indicating that any kind of data flows back to Moodle from the LTI-provider. e.g. about lessons. (the lessons are available in separate activities imported via an IMSCC-file)
Another test I made was to set up the external tool in my own development Moodle 3.6.4 where the settings for the services are available in the tool configuration. But the grade synch does not work there as well.
In the end the whole structure may need to be implemented in a Moodle 2.9 with LTI as a plugin. But no tests were made in an older Moodle yet.
Since the Moodle 3.4 where it works is "in between" the two versions where it does not work, I suppose the version of Moodle is not really the source of the problem.
What could be, though, that we have not tried yet? A server setting? Some Moodle setting? Both the 3.2.2 and the 3.6.4 Moodle are mostly "out of the box" with no special settings or exotic plugins.