My farm is located in a Deep Ocean Biome.
Ugh! Darn you ticket search engine! It is the same. I did a search but wasn't clear enough I suppose.
In single player survival with elytra and rockets. Mostly happens when diving straight down, but has also happened when flying straight up and horizontal.
@jeremy ruddock Can you tell at what y value the guardians are spawning in your experience?
I would love to be wrong about this. Perhaps something is corrupt in my world somehow. I can always build a new farm IF Guardians are actually still spawning.