Why on Key agreement the check when all z xores are 0 not performed

[pc-magas]

According to documentation on group key agreement the following check seems to be ommited: z1⊕ . . . ⊕zn = 0 whilst mentioned on original Pointcheval's GKE+P protocol.

So I wondered why is ommited? I also asked upon this as well: https://crypto.stackexchange.com/q/66544/59291