Minecart with hopper will despawn if within a block

On my realm I have a mob farm, recently I noticed that the minecart hoppers which would collect the drops were missing. I thought this was an update issue but when I replaced the minecarts and left the area and returned, they could not be seen. I checked if they had left the block, but they were nowhere. I tried to replicate this on a singles player world, however the issue seems to only exist on realms.