Wow! Four weight pouches lost over 60 dives? That sounds like an incredibly high failure rate. I'm trying to imagine any common factors, beyond just the make & model of weight pouch.
Did the failures happen only on tank 2 or tank 3, or on the first dive as well?
Could there have been one person who inadvertently mishandled equipment in such a way as to unlock the weight pouches from multiple divers? Did divers remove BCDs in the water and the crew brought them on board after divers surfaced? Was this "concierge" diving, where the crew swaps BCDs over from one tank to the next. Was there a crewmember who was trying to check weights as they helped divers get off the boat?
Could there have been anything about how BCDs were stored before dives that contacted the weight release (for example, the height of a bungee strap in a tank rack, holding assembled BCD+tanks between dives)?