Fun quirk: floating spikerocks
This isn't a problem, as far as I'm concerned (whether or not it's technically a glitch), but there's some amusing behavior with spikerocks on Pirate Seas levels: if you bring a spear-mint to any level with at least one row with "missing" planks, at the end of the level, before you get your rewards, tap and hold the spear-mint over the lawn. Once the rewards are granted, drop it anywhere on the lawn and (assuming your mint is leveled up enough to fill at least one column), it will fill the tiles between planks with floating spikerocks.
I see it as a harmless and entertaining glitch.
This end-of-game bug has been for many years now, besides the one you are showing, you can also plant most instant use plants (for example, Cherry Bomb) on the water and see its expression and costumes....
Have fun. 👿