This phenomenon is fairly easy to recognise and can occur with nearly every type of casing soil. The mycelium stops growing and seems to be creeping against the layer of casing soil. During recovery mushrooms fail to develop nicely and in the worst case discolouration occurs in the first flush. This problem can be quickly identified and solved.
Regularly check mycelium growth in the casing soil when the casing soil is sprayed especially during the third or four day. Take a handful of casing soil each day and examine the lower layer carefully. If too much water is collecting and if casing soil sticks to the compost when removed then caution is recommended. To avoid this problem, do not spray too much at one time. Preferably spray little and often. In practice this means not spraying more than 2 litres each time and leaving a long as possible interval before spraying again. The total amount applied to the casing soil can be slightly reduced, but never more than 2 to 4 litres/m2 in total. Sticking to this routine and regularly inspecting the casing soil should help avoid problems.
Henk van Gerwen, AdVisie ‘The mushroom cultivation advisors’