Those need good drainage, would not be likely to hold up better in a damp situation than the laurels. Probably you have a pathogen at work, perhaps honey fungus (Armillaria). The way it appears to be moving down the row would fit something like that. See about getting diagnostic assistance from California Cooperative Extension. They have had a large presence on the internet in the past and will also be present in telephone directories. Substantial amending of planting hole backfill in damp soils is liable to produce sump-like conditions, make the soil around newly planted specimens wetter rather than drier. Digging in amendments around existing shrubs would be expected to result in damaged feeder roots without adequate improvement in drainage.

If these are Prunus laurocerasus I would take issue with their requiring acidic soil. They are becoming a weed tree in woods here on most soils. You don't say where you live so it's hard to know what temps these have been subjected to. Here they will grow in quite dense dry shade such as under trees so I wouldn't expect them to enjoy heat. What cultivar are those? They seem very small. Are they a dwarf such as Otto Luyken?

Since Cherry Laurel is an evergreen, maybe it's just time to push a new set of leaves. I only have one and don't pay close enough attention to it. The Live Oaks leafed out in April, Magnolia seems to straggle along all summer.

pic would really help .... dry shouldnt be an issue on 7 year in the ground plants ... i would wonder about frost or freeze.. since they leafed out ... where in z6? .. great variances ... how bad was your winter ... i had a z4 in my z5 ... my cherry did not take it well ... but it hasnt leafed out yet ... good.. since frost is possible tonight .. one might think.. it has to be cold event.. if all 3 are showing the problem .. for a disease to attack all 3 ...... in early spring.. seems off to me ken