S. African grower,
It appears you haven't hardened off your seedlings first before placing them into the soil, especially with expensive or rare seeds you must babysit them for a bit before they go into the ground, you want to give your seedlings the best advantage by sprouting them very early in the season if possible because the plants must develop some before the sun reaches a high point in the sky, it's kind of something you you'll want to place some importance on, because an under developed plant will suffer the consequences for the entire grow season, and many get consumed by the sun's heat mid season.
I'd recommend sprouting them in containers and keep them in light sunlight, kind of partial shade but not where they experience long hours of shade while the sun is out and screen out some of the light, but avoid direct mid day sunlight early on until the plants are a few weeks old or more, kind of just a balanced filtered light is what you are looking for, similar to what a seedling would experience at the bottom of the forest floor and the filtered light from through the tree canopy above.
If you are sprouting seeds late in season I'd recommend putting them in larger pots the entire season and keep them where you can control their growth, and amount of mid day sunlight and so forth.
But also about the soil, it needs to be lighter and not so dense for a seedling, this soil you have in the pics needs a bit more organic material added, even straw would help aerate the soil and aid in moister wicking the soil a bit, better for growing deeper roots.
Have you tried growing legumes in close proximity to your plants for extra nitrogen, peas and beans and such? In nature plants provide for each other and offer benefits, while science would like us to believe that it's all survival of the fittest and competition, the truth is in a controlled environment many plants can offer benefits to other plants and trade energies built up in the soil back and forth with other through terpene signaling, terpenes must be present in the soil already before your Cannabis plants can synthesize it's own.
Anyhow sorry to hear about your losses in seeds, and I hope you can recuperate and experience some nice plants soon.