Rule of thumb is: Golf ball to a pea ratio. Mix 50 gms of filler paste to 1-1.5 gms of hardener.
There are several reasons for pin-holing such as poor mixing technique, usage of body filler on porous surface or wrong storage. Thus, make sure to check surface to be even, dry and clean. Use a gentle folding action when mixing the hardener to avoid adding air. Store at room temperature (20°C + / - 8°C).
Please check the following. Did you select the correct product for the surface? Alternatively, wrong surface preparation e.g. no cleaning (area needs to be free of wax, grease or other contaminants), excessive temperature or usage of hardener might be the cause.
The reasons can be manifold. Insufficient usage of hardener (use of too little hardener can cause rollback of the product on the thin edge of the application area) or too little mixing might be the reason (filler paste and hardener do not create a uniform texture). Also, incorrect application temperature or storage temperature might be the reasons. See the TDS for that.
The reason for this could be that the wrong hardener was used (with TEROSON products always use the included hardener). Alternatively, too much hardener was used or an inadequate mixing technique applied.
The depth of the hole might have been too deep for one application round only. Make sure that either the maximum sanded depth is approximately 3 mm.