The only times I have seen these conditions before was when a major restriction after first plates increased their pressure or when freezer plates have no eutectic solution in them. If the freezer plates are SeaFrost’s vertical cast aluminum plates the front cover sealant has failed before allowing solution to leak out. For a -20 C solution plate to freeze solid suction pressure on this type system needs to reach a vacuum of 9 inches. What is line temperature after each plate when compressor suction pressure is 4 psi or lower?

I would use a #1 orifice as it reduces fluid back problems although it extends first days pull down time. A #2 orifice will better match combined eutectic plates Btu capacity.