Various miniature orchid issues

[estación seca]

Lack of air circulation is a big problem for terrariums. I would suggest improving that.

Plants don't grow without fertilizer of some kind. Once a month during the growing season isn't enough. The plant might have been coasting for a while on nutrients remaining from the previous grower. I would definitely increase the fertilizer.

You don't mention what kind of water you are using. Most of these cloud forest orchids need very pure water, like distilled, rain or reverse osmosis. If you're using pure water you very much need to fertilize, as well as use a calcium and magnesium supplementation, since these elements aren't usually in regular fertilizers in adequate amounts due to solubility issues.