My girlfriend has a 2016 Traverse that she bought in 2017, with low miles on it.
Has been a very good vehicle, no issues at all, with 97K miles on it now.

Recently, (over the past month or so), the A/C would still cool, but the air was noticeably not as cold as usual on hotter days. Because it is a 3 row SUV, with the ductwork in the roof, it would always take a minute or 2 to start cooling really well, but it would always get very cold fairly quickly. Instead, it just seems to get moderately cool.

I figured it may be low on refrigerant, so I got a recharge can of R-134a with a gauge on it, and the low pressure port reading (while running) was around 24 PSI, maybe a pound or 2 below the minimum / normal range of 25-50 PSI.
I could only get about 2 pounds into it, even with several tries, no more than 26 PSI. That was within acceptable range, and I figured maybe the can was not pressurized any more than that.

Ok, so it seemed to cool a bit better, but still not like it used to. About a week later, she said the A/C would not come on at all, when she pushed the A/C button, instead of it lighting up, the button would flash 3 times then go off. She took it to a shop, and they checked it for leaks, and determined the Schrader valve was leaking, so they replaced it, evacuated the system and recharged it. She said the A/C worked good for 2 days, and now it is doing the same thing, A/C button light flashes, then goes out, no cooling. I have not had a chance to take a look at it, but she brought it back to the same shop, now they are telling her it may be the compressor. I do know the compressor was engaging and running when it was only cooling moderately, and also verified that when I recharged it.

Any ideas? Doesn't seem like the compressor would be the issue, they usually work or they don't, from my experience.

Thanks in advance for any advice on what to look at, or possible causes.