Hi C,
I tried deleting all old courses events (leaving just assignments events), and again, no luck.
As you said, the last option is to delete half of the old courses but it seems far fetched as our site has less then 60 courses. I feel like we are missing something because there is no way that this problem is not a big issue for bigger organizations.
We are using More theme for now and planning on switching to Evolve-D in few days.
BTW, some of our courses are in Hebrew and some in English so we can exclude languages too.
My next test is to export reports and check there.
Cheers,
Ohad