I am reading this post with interest. Looking at the pictures it does look as if you have used enough adhesive but the adhesive has compressed and hasn't taken a bond to the ply.
Personally I would use the same batch of plywood. Do a control test, I.e use the same weber adhesive and fix one tile to the ply. Then use another adhesive (bal, mapei etc) and fix another tile to the ply. Make sure you use the same ply that is on the floor as that may prove the ply is at fault, if however one of the other adhesives take to the ply then the weber adhesive is at fault.
Hope you can get this sorted out.
Personally I would use the same batch of plywood. Do a control test, I.e use the same weber adhesive and fix one tile to the ply. Then use another adhesive (bal, mapei etc) and fix another tile to the ply. Make sure you use the same ply that is on the floor as that may prove the ply is at fault, if however one of the other adhesives take to the ply then the weber adhesive is at fault.
Hope you can get this sorted out.