Hmm, 23 days ago I had a guess at the problem, but I can't remember what it was anymore. (Reading what I wrote, I must have suspected that they are being properly loaded for cohort definitions, but not for data set definitions.)
But since your logs never show that file being loaded, the error must be earlier in the process.
Any chance you can run this under a debugger with the reporting module code checked out, put a breakpoint at this line, and see what directory it's expecting?
(If not, make sure that the level of debugging output for the reporting module is at least INFO level to be sure we're not just missing the message for that reason.)