Usually the story here is that the "flame sensor" does not find any flame so the whole thing shuts down right away. (as you suspected in the OP)
You said you put in a new "igniter", but did that include a new sensor?
Newer "igniters" do not have a separate sensor electrode, but instead they measure flame between the igniter electrode and the other prong where they spark. That signal goes back to the board.
So whatever you have it is still no flame sensed by the board so it shuts off the gas to the burner.
New "igniter", board checks ok, so IMO suspect the connections from new igniter to the board are not properly connecting.
30 seconds is a long time for that though?
