This crack may well have started as a check but but was encouraged by the thrust from the common rafters at the sides.
If it is a dovetail conection at the Tie/plate then you would get some give in the first weeks after assembly as a result of some slack in the fit as well as compression. This could be as much as 1/3rd of it's total movement. In the years following as the dovetail dries and shrinks, the plate would then be allowed to further separate.
On the bottom of the Tie at the back side of the post there seems to be a rather large gap in the mortise suggesting perhaps the inside portion of the post has been pulled out. I am puzzled why I don't see any pegs at that post to Tie M/T.