Alright, so I reproduced the flight one last time, and as usual, the cabin pressure started to increase.
I forgot to mention that I did attempt resetting the bleed valves on the ground, but nothing happened. During this flight, I held the bleed switches on RESET for at least 5 seconds each, but nothing changed.
The Pressure Dump switch was off. Reaching 10,000 ft, I was about to take a screenshot of the overhead when I noticed that I was still getting a warning that the bleed valves were closed, and the warning panel was notifying me of AIR COND(with the up arrow), so I decided to try and reset the bleed valves one more time (this time by holding reset for a much briefer time), and to my surprise, it worked. The cabin altitude slowly began to drop, I continued with my flight with the cabin pressurized and a max diff press of around 5.X
What I didn't understand though was why wasn't I able to reset the valves on the ground? Am I supposed to engage them after I get the engines running? Every time I tried doing it on the ground during the Before Engine Start check, the warnings were still displayed.
Anyways, thanks devs for the help, and I am very impressed with your aircraft (despite being underpowered)
-Omar