Hi, Ralph. Thanks for describing your tests in more detail. You seem to have established the precise circumstances that produce the effect.
The reference I looked at said that the Metz 48 AF-1 does Multi, but accept that it doesn't.
I do not have the Strato triggers, but my Pixel Kings try to build up a map of the attached gear and act appropriately. They do not always get it right.
The biggest problem is with the hotshoe/hotfoot, which today is stretched way beyond its suitable use. Dirt, looseness and improper mounting cause many problems, and can be remedied by the user. Differences in engineering dimensions can produce mismatches. I'd check the Strato shoe and Metz foot, looking for any risk of intermittent contact, particularly on the rear pins. Then thre Stato case would be opened and the connections to the shoe checked. The more advanced these devices get, the more they require perfect conditions.
Oh, and batteries. Another major problem. Quite often, the batteries in new units are barely functional (low cost), and should be replaced on arrival.