Iran blocking of direct users, 2016-08 and 2016-09
Direct users in Iran dropped from 8,000 to 2,000 between 2016-08-20 and 2016-08-23. The numbers recovered to 4,000, then crashed to 400 on 2016-09-03 and 2016-09-04. link
Edit 2016-10-04: the bridge changes below, on further investigation, appear to be unrelated to anything done by Iran.
Looking at bridge users, there is an increase right around 2016-08-20, the time of the first blocking, then an abrupt return to previous levels around 2016-09-03, the time of the second blocking. link
Looking at the graph of bridge users by transport, obfs4 continued working while obfs3 and vanilla were blocked. link