There are two bloc spaces where I cannot place blocs, they will only appear for a fraction of second before disapeering. In survival, the blocs are consumed. entities such as minecarts will not enter said spaces, even when nudged, and zombies will glide out of them. this appeared at an unknown time, without interaction (I noticed because a minecart supposed to go back and forth at this place stopped moving when on active powered rails.
This will also prevent a hopper set previously under the problematic area to pick up items.

I can push a bloc inside with a piston, or setbloc/fill a bloc into it, but the problem remains as entities wil avoid the area, and when the pushed/setted bloc is broken, it is still impossible to place a bloc normally.

Attached are screenshots of the problem (minecart bumping into nothing and going back, minecart flotting above air and hopper not picking items up).

Concerned areas are blocs -37 54 398 and -37 54 397. see chunks extracted via mcedit in zip file. (before comes from backup save, after is save after bug is noticed and experimented with)

EDIT : After reloading the map, a minecart had appeared in the spot of the problem, and the bug does not not seem to be present anymore, I would still like this issues to be looked upon, as entities disapearing and preventing bloc placement (and here, breaking a contraption) is quite a bugger.