Terraforming does not require any TN minerals.

Well first of all, 0.08 is really far from 1. Second of all the terraformers only check if they reached the max atmosphere at the end of the increment, which means it will always go over the max atmosphere.

He meant 0.98.

Just to say, at the topic, understaffing won't cause the terraformers to shut down, simply to run less efficiently (you won't be pumping as much gas into/out of the atmosphere as your terraformers are capable of).

Terraforming isn't perfectly accurate.   If you set oxygen to be at 1. 0 atm, you'll often end up with 0. 08, 1. 02 or whatever.   

In my current game, i had a planet where nitrogen was supposed to be at 0. 9, oxygen at 0. 21.   
In fact, nitrogen reached 0.  902 and oxygen 0. 2194. 

However, the difference is always negligible and it will never jeopardize your terraforming attempts.

Well first of all, 0.08 is really far from 1. Second of all the terraformers only check if they reached the max atmosphere at the end of the increment, which means it will always go over the max atmosphere.

I'm going to hijack this thread with my own information.
I ran into this problem recently:

I was terraforming Mars.
I had 10 terraforming installations and ~5 10 module terraforming stations in orbit.
I was adding oxygen with a max value specified at 0.1 atm.
At around 0.08 atm of oxygen the terraforming just 'stopped'. No messages, not notifications. I only discovered this because I manually checked the environment tab of Mars and saw that the gas dropdown was set to 'Terraforming Inactive' (or whatever the wording is; don't have game in front of me now).
I had to re-enable the terraforming for it to continue.

Note, I did NOT check the population status at the time, meaning, it is entirely possible that I was running my installations understaffed. Is it possible that the terraforming just shut down due to lack of workers? Again, I got not messages or notifications; and, I had ships in orbit that required no on-planet workers.

Also note, I am fairly certain the population was well above that necessary to run the ten terraforming installations. THey would have required... 2.5 million workers; even accounting for the service sector, agriculture, and the limited number of construction/mine installations I am fairly certain I had plenty of workers at the time.

Given all that, I would like to be confident that it was not understaffing that caused the issue, and as such I cannot figure out what else may have caused the issue...
I had ~200,000 wealth, so even if I was running at a day to day loss I would have been fine, I had plenty of infrastructure on the colony and it was not over-populated. I am NOT sure what the protection rating was, but am I correct in thinking that colonies under 25m don't have a protection requirement? (I may have made that up right now)...

Does terraforming require minerals? Mars only produces extremely limited numbers of like two minerals; that said I never got any insufficient mineral events regarding terraforming that I can think of, but, it is possible I missed one since I've been fighting Corundium shortages so those types of messages are pretty common and easy to ignore.

Maybe with that info we can figure something out.

Need more info.

Did it tell you any message? It's possible that if you set a limit on the maximal atm, and it hit that limit.