- Create a course backup file in Moodle 3.5.* or 3.6.*
- Restore the course onto a Moodle 3.7.* or current 3.8 dev. (also perhaps when a Moodle 3.5 backup is restored on a Moodle 364/365 site, though this has not been so systematic in my tests)
- Notice that Assignment Due dates and Due to be graded dates are NOT showing in: Course calendar, User calendar, Upcoming events blocks (Dashboard or Course), Timeline block. Likewise, the closing dates for Choice, Lesson and Feedback (sometimes possibly Quiz ?) are likewise missed. I have NOT tested other core activities, just these five listed / mentioned (plus the Questionnaire plugin, which seems to work OK at least with the Calendar.)
- Teacher must either re-save the affected activity or at least re-name it on the course page in order for the mentioned blocks to pick up the dates. To "cure" all the affected activities of a restore course in a single step, course reset must be used with a course start date activated (not necessarily different than the one currently found in the course settings).
The described problem does not appear to affect Moodle 3.6.5, which I have also tested. NOTE 2019-07-13 00:41 - Not true, i reproduced the error on M3.6.5 as well by now. NOTE 2019-07-13 23:33: After more testing, I find M365 to be producing more reliable results, while the 37 and 38 versions always fail.
It seems that sites upgraded from Moodle 3.5.2 to a higher major version do not "lose" existing calendar information. However, the problem affects course restores across platforms at least, so it appears serious to me.