Question about harvest

[Reis]

So I was shiny hunting salandit and magikarp on 2 seperate occasions. I had skill swapped harvest onto them and tricked a leppa berry so they should be recycling the berry. However on both occasions, harvest never activated and they struggled to death. I checked their move set and none of them had any self-damaging moves, so struggle is the only thing that could've ended them. Am I missing something about harvest, like does it have to be at day for it to work?

[Chansey]

It always activates in harsh sunlight but only sometimes without it.