Any of the above could be a contributory factor but not actually very likely if that makes sense!!
Ivory side down for boards yes, but if they are not it does not really make a jot of diffrence, the tapered edge of the board is ivory side out hence fixed this way.
Can I assume this is a new house on a newly built estate, if so the materials will be compatable as the deals would have been made with who ever and the full quantities delivered shrink wrapped to each house as the spreads go in.
Other reasons for this to happen include dirty gaugeing water, old past its best plaster, retempered mixes instead of fresh for second coating, and overworked finishing where too much of the splash brush has been used for polishing off but theese would normally be for the odd wall or ceiling rather than whole sale.
Therefor my opinion is that, as was common practice a few years ago when rates were poor many spreads would only one coat boardwork and if large areas were hit on one gauge they would cure quickly and need alot of splash brush to bring them bak for polishing, not great practice but the diffrence between a decent wage and half nothing. this left boardwork with a poor bond and liable to shell but the man got paid and thats all thatvconcerned him.
Lectrician your problem is the render coat has cured too much before a skim was applied so the finish would take up (dry) almost on contact with the wall, the second coat would be workable only for a little longer and could be polished up but the bond is not there initially. Browning should be skimmed the afternoon after application and sand/cement the following day.... regardless of what manufacturers may state!
Preperation is the key to good plastering!