They will swell & contract with temperatures & humidity levels.  

The property is located in an area that has very high Humidity in the summer and freezing winters.

Identify where the moisture/humidity is coming from.2.)

No disrespect here, I am not saying that your work is messy, especially without seeing it, but working in the business I can tell you that most drywall guys particularly finishers claim that any work that they have not done themselves is F*ed up “looks like a beaver to cut this board” and “did you spread this mud on with your face cause it’s almost as ugly” are two quotes I remember that don’t involve inappropriate comments about the size of the gaps in seams.I also agree if you are looking for perfection and to save time hire a pro, if not… try using the 20 and 45 min bags just mix what you can use before it begins to set and if it is very humid where you are working invest in a dehumidifier I couldn’t believe how much quicker everything dried; I was able to get 2-3 coats on a day, long days...if it is in the budget hire a pro.

In addition the humidity is higher usually in basement units and you have to be concerned with formation of mold. 

(i'm afraid of the humidity there as it caused in Tampa several issues with our investments) What about Arizona, like phoenix, or Utah like Provo ?

Does it get worse with humidity?

Looking forward to the great migration from West Coast to East Coast. but then you have to live there  humidity storms no mountains.. who wants that  ugh. !! 

The oak flooring had buckled from humidity.

Thanks, Rolanda, how is the humidity?