Unlike previous versions, as of 1.16-pre4 or 5, turtle eggs only hatch when placed on any block with either regular or red sand underneath (blocks with the #sand tag), so the game does check one block too deep. This issue breaks all turtle farms containing only one top layer of sand, and for example a hopper minecart running underneath.

To reproduce this, note that turtle eggs hatch significantly faster towards the end of the night, a higher randomTickSpeed setting speeds up the process too.