Hello again, it does indeed sound like the check valve is bypassing liquid and is driving the suction pressure up. If the check valve you are talking about is fit at the indoor coil, it can be removed, and capped off since the system can no longer go into heating mode.
Before you do that however, I would like to see pictures of the capillary tubes and check valve, taken at several different angles and taken from about 5 feet away so that I can see how the entire coil is piped in that area.
Another picture that shows all 3 compressors, taken from about 10 feet away so that i can see all 3 compressors and the suction line piping will be helpful as well.
You can use the paper clip icon at the right end of the tool bar above, or the '+ attach fines' link to the left of your 'send' button to send me the pictures.
With such a hot building inside, 35C, I would expect the suction pressure to be high..
Tell me what the other stage suction pressure is running, and very importantly I need to know if the suction line on that compressor is running cool, cold or sweating.
We can go from there.