The surrounding air becomes denser very rapidly and squeezes those thermals until they pop like a teenagers' zit. The right thing to do in this situation is to fly the wing and keep it fast. Pull it in and DO NOT TRY TO SLOW DOWN because this will exacerbate the potential stall when you hit the outer regions of the thermal where the wind shear is the greatest, and if you stall that low in descending air you can easily impact the ground before any opportunity to effect a recovery. I have been there and done that in hang gliders more than once and most recently last July flying in British Columbia when I nearly ate a landing light for lunch landing on the runway at an aerotow flight park. I am convinced this is what he experienced because of your description of the conditions as being turbulent and causing alot of rolling and pitching.
Turbulence is atmospheric mixing and thermals are the primary mechanism of atmospheric mixing.