I have 50 seedlings in the same tray, with the same soil and the same feeding regimen, all from the same batch of seeds.
If it's transferrable from parent to offspring I would suspect it not to happen in certain cultivars, since those trees are grown at nurseries from either cutting or seed and the parent trees need to be healthy for both. But my norwegian type sylvestris does it, my mugo's do it, my J. red pines do it too.
I did keep a good look at how it progresses:
Starting point is multiple buds on the same location.
The buds throw juvenile foliage, half of it dies. They grow at different rates.
They form new buds in fall or winter, as a super dense cluster.
The buds wake up in spring and soon die in the second year, usually around summer. They die naturally by turning brown and shriveling.
Thinning the cluster seems to be beneficial, but it's no guarantee that it'll live. If it does, it returns to normal in the third or fourth year.
Could be something viral, bacterial, witchbrooming or something. I'm suspecting something bacterial.