spiral yew
I upgraded this city, which originally had a Moth egg inside it, and got a Centipede. Instead of being pushed to one of the empty land tiles, it was pushed onto a water tile without algae.
When the egg hatched one turn later, the resulting Larva also remained on water.
tiny cradle
I'm pretty sure the port is the problem, not the egg. It isn't checking that the port will decompose and allows the land unit (the egg) to enter a tile that land units can usually enter. A problem that I'm guessing is very similar existed after the Aquarion rework, where regular units that Aquarion mindbent could walk on ports without becoming boats.
@halcyon latch More special tribe/port interaction issues.