Is this air pocket something to worry about and it is a High end custom Aqariums it is 64x26x26 and it was there from day one tank is ban up tuning for about 2 yers
I wound contact the manufacture ASAP. I would also drain the tank, it’s not worth the cost to have it fail and flood your room. I had a Red Sea tank with an air bubble, and they replaced it without question.
It has been up for two years, so I wouldn't be crazy concerned. If you have a solid flat base for the aquarium and it doesn't move, I think you are good. Be careful though adding wave makers.
Not sure why you wouldn't have replaced this sooner. Of all things this is definitely unsightly.