Having done away with the invite system they seem to be struggling to meet the demand for the OnePlus 3 which still seems to be as popular as ever, and they just can't make them fast enough to satisfy the demand.
A lot of folks on the OnePlus Forums are also upset about the dispatch times currently being quoted, but the general feeling seems to be that it is a phone worth waiting for.
I can be very frustrating to hear about folk who ordered a few weeks ago and received their phones virtually the next day, and then to be told that there is now a three week wait for them!