(1) Searching by courses sorting options don’t seem to be accurate. I very often filter by “my imports” and sort by “last imported,” and results are hit and miss. Very often, courses seem to be simply left out of the list completely.
(2) I have added so many lessons to this course that I don’t know really how many there are: https://www.lingq.com/en/learn/ru/web/library/course/1408611. I seem to have reached a limit, because the most recent lessons I tried to add to the course simply disappeared! They are nowhere to be found.
That a course might have a limit to the number of lessons is very reasonable. However, just throwing new lessons away with no warning or explanation is a defect that needs to be corrected.