When I dived down into the files, I found out that the project Targeted Outgassing, has a condition of pressure being between 0 and 1 to allow you to increase pressure to 5.
I believe it should have been between 6 and 8 since it is supposed to remove pressure from the atmosphere.
The current pressure is impossible to achieve, since there is no way to reduce atmospheric pressure to 0.
Also, there is currently no way to increase the air pressure other than melting the ice event.
This problem disallows players from finishing one of the terraforming missions atm.