Thanks very much guys. Here is the reason listed by the case officer in my document request:
"I have concerns that you have accumulated at least one year of full-time work experience, or the equivalent in part-time work, in the occupation identified as your primary occupation, specifically NOC 4012. Specifically, I have concerns regarding the genuineness of your work experience at the University of Toronto because the letter of employment that you have submitted does not provide any details regarding your working hours."
So TA experience doesn't count towards CRS points (out of 1200) but will count towards FSW points (minimum 67)? For the letter of support from my department/supervisor, should those letters attest to the fact that I am working full-time (either as TA, CI, or RA)?