When using heavy soils like MG, it's important to choose containers that are proportionate to the mass of the plant material. Heavy soils will have a completely saturated layer at the bottom of the container that impairs root function/metabolism, and can quickly cause root rot. Since peppers need good drainage, you need to be very careful how you water, at least until the plant has matured and roots have colonized the entire container.

Of course, it could be another issue unrelated to soil moisture, but if it is, there's not enough info in your post. Did you fertilize? With what/what strength?

Drainage isn't related to the number or size of the hole(s) in your container. 1 hole or 100 doesn't matter, as long as water is free to move out of the container through the bottom. You might consider using a wick to help remove excess water after you water.

Al