You have a crappy protein!
Easiest way to discuss it is via beans. Beans have a protein in them which humans cannot digest. We can't, but the BACTERIA in your intestines CAN. When the bacteria munch on them they then produce GAS which you spew out the easiest exit port.
The same thing happens with protein powders using cheap/inferior proteins. You get proteins in the gut which you can't digest, but your bacteria can.
MORE fiber might make it worse. The enzyme in beano won't work on the inferior protein in your drink unless of course it's the bean protein they are cutting into your powder.
You need another protein powder.
The same also happens with RAW eggs because there is a protein in the raw egg which the body can't break down, but cooking breaks it and you have no problems. If you have egg powder in the protein, this could be the problem as well.