Hi, I haven’t seen this behavior in 5.5 (I haven’t got Floxy but have been testing HISMs)
I just made a test scene, a simple BP with a HISMC and a function to spawn 50 cube instances, then another BP with a “CallInEditor” function that gets all the first BPs in the level and calls the Spawn function (so that the construction only gets called on the 2nd BP in the level) - it seems to work correctly.
How are you spawning the instances? Does a simple test like this work ok on your hardware?