Pure coco will retain more water than soil.
OP has mixed 30/40% perlite which should help. My concern was actually way more about the plastic pots as they don't breath well - even with holes.
It would make sense that it only an issue now (mid-winter). It is colder, so less evaporation happens off of the soil medium, and the plant transpires less because it is cold. Which means the plant pulls less water out of the medium.
To give an example, I have other plants I grow in plastic pots. I had to water them everyday in summer, and only once a week at the moment - I actually killed a plant by water twice a week at the moment.
However, it could be something else, the only way to really test is to see if the same thing happens to the fabric pots in the same circumstances