Any fish that is stressed will not act normally. Usually they will stop eating, will into swim freely in the tank, might hide or swim only near the top or stay hidden behind things in the tank.
The most stress free way to deal with guppies or any livebearer that I have dealt with is to have plenty of plant cover in the tank. Java moss, Java ferns , water sprite are all low cost plants that live in most tanks, even with low light conditions. These will give the fry places to hide and I don't usually worry about putting the females in a breeding box.
If I really want to protect the fry, I place the female in a separate tank....let her give birth, then remove her from the fry tank....
ANY water conditions with any
ammonia,
nitrite, or high
nitrate will stress any fish and needs to be corrected, with water changes and proper care through the
nitrogen cycle of the new tank.....Best to cycle fishless and do all the water tests to make sure it is complete BEFORE adding fish......