Alright I had some time to mess with , and while I’ve not yet confirmed that the spikes are gone, I got the area that before I was unable to ‘smooth’ or sculpt into or on, to work again by flattening the whole area. Odd ?
I’ll update if the spikes are gone.
later
nl
So those spikes from the first post are still here? -> have you already tried it with the 4.7 preview 
I didn’t have time to verify the spike,I just verified that the areas that would not allow me to sculpt or smooth ( brush stopped at ‘edge’ of that area, very odd ) previously is fixed. I just took flat brush and flattened them to ground, but it didn’t go quietly, it took many back and forth stroke and it fought me every inch of the way .
SO ya, I’ll check it out now and see if smoothing no longer causes spiking,one sec:
Yes , the smoothing is gone whew…I guess the was area on terrain that brushs wouldn’t go through , end to end. Very odd ?
Anyway I wish I knew what it was but so far I can’t duplicate it.
Cheers
nl