I had trouble making slope MHMs and finally found the problem was because Meta was bending the MHM quads in the opposite direction from my MSM floor quads. (see picture) If you use Meta's 'wire' tool to set the bend direction by dividing the MHM 's quad into triangles, you might fix some troubles.
SoM also had a defective MHM on the 1M slope wall pieces (fixed in the v1.2 patch) and there was a lot of bugginess in the outdoor floors because they aren't flat; they're a low pyramid shape which doesn't work well for collision. I have .5 and 1m slopes in my forest that use simple flat MHMs and haven't had problems so far.
SoM also had a defective MHM on the 1M slope wall pieces (fixed in the v1.2 patch) and there was a lot of bugginess in the outdoor floors because they aren't flat; they're a low pyramid shape which doesn't work well for collision. I have .5 and 1m slopes in my forest that use simple flat MHMs and haven't had problems so far.