Steps to reproduce
Place 2 solid blocks, one diagonally up from the other.
Place a boat on the lower block while pointing the crosshair within about 1/4 block width of the edge nearest the upper block.
Expected result
The boat rests on the lower block.
Actual result
The boat falls through the lower block.
When you spawn a boat in a corner (as shown in photo) It falls through the block you spawned it on. If you break the block you spawned it on and ride it there is a little section where you can see through your world but go any further and you will suffocate.
Note: By the way I did this in creative
This behavior existed before 1.16 and was reported at MCPE-58008, but we were not able to reproduce it in 1.16.1 so that report was resolved. The behavior seems to have reverted in 1.16.100 or 1.16.200.