I think location could be a problem here.

2 years back I planted corriander in a grow box filled with only compost. The box was located in a shady position but got a few hours of sunlight until about afternoon ( this was becuase a wall blocked the rest of the sunlight)

So these corriander grew really well. Lush green leaves a good size too. Cut them off and they grow back but not as well. But seeing as I had a whole box I wernt too bothered.

So the year after, same box, new compost. But location was different. They recieved a lot more sunlight. They grew really well with lush leaves to a height of about 4 inches. But then they just started to wither. The leaves went light green and the corriander went to seed. The soil was always kept watered like the previous year but they still didnt grow so well.