If you put a trapdoor next to a pressure plate, then sneak in between them (you should've activated the pressure plate). You'll discover that you can walk right through it! This can occur with all trapdoors.
Linked issues
is duplicated by 4
Attachments
Comments 2
Relates to MC-227095
The collusion box changes to inside you, this is not fixable/not worth the effort.
That pressure plates trigger from that hight is a valid issue though, create a different bug report for that.