I'm experiencing pretty much the same thing. My kid hosts our game from his account for the rest of us in our house (host + 3 clients). Everything appears fine for the host, but all 3 of us clients end up with some structures in the game being invisible after completing crafting/repairing. This doesn't happen for *all* new crafted items, but somewhere between 25-50%, which makes the game unplayable for the rest of us.
On any of the Clients:
open Crafting menu and select a "Grass floor" (or anything really)
blueprint 4 grass floors straight out from our house
chop down some grass and build out the blueprinted floors
Behavior from the Clients' perspective:
for 1 or 2 of the grass floors, as soon as you place the final piece of grass to complete the build, it vanishes
unable to build a new floor in that location because technically there is one there
however, you're also unable to snap new blueprints to the sides of the invisible floor because your client thinks it doesn't exist (previously placed blueprints will stay and be supported as if the invisible floor exists)
when walking over the "invisible" floor, you fall through as if it doesn't exist
once you walk far enough (e.g. taking a couple steps to the left or right) you ultimately rubberband back up into the air where you would have fallen off of the invisible flooring
From the Host's perspective:
all the floors appear just fine
when the client walks onto the floor (step 4 above), they don't fall through -- they're just standing on the proper floor
when they walk around (step 5 above), you just see them walking on the floor until they eventually walk off the side