I hate virtually everything about this hand.
Really, ranking the mistakes is quite a job. The LAST mistake, and the one that forgave all the bidding mistakes by EW, was the lead of the
♣Q. That was the biggest mistake in terms of the score.
Probably the biggest blunder in the bidding for EW was the forcing pass of 6
♠. This guarantees first round control of spades (and may have influenced North's unfortunate choice of lead).
I understand the RKCB bid by East. East no doubt assumed that the opponents had at least 9 spades between them so partner had to have one or none.
Despite the forcing pass, East should not bid the grand. EW is missing a key card, and the forcing pass, while guaranteeing first round control of spades, does not guarantee a void. If West has the (presumably singleton)
♠A, then EW is off a cashing ace. One does not bid grand slams on speculation.
W - N - E - S
1♥-2♥- X -3♠
4♦-ps-4NT-ps
5♠-ps- 6♦-6♠
ps-ps- 7♦-ps
ps-ps