When I try to place blocks at a high y-level (in this case for me y=254 and above), it will usually remove the block and return it to my inventory after a half second. Blocks can be placed occasionally, and it seems to be only on blocks that were placed longer ago. In addition, when the player places a block, for the duration of the block being put down (if it will disappear), the player begins to suffocate. I am on Realms in normal survival.