Answer: Unfortunately, based on your description I am not certain what has happened. Sod is usually laid on top of bare soil that has been thoroughly prepared and the surface raked smooth. If there is a layer of what seems like thatch under the sod, then either the initial preparation was inadequate, or possibly you are looking at dead roots (roots of the sod) that never grew down into the soil. Sometimes, if sod is not watered correctly, it will shrink and reveal "seams" between the sections of sod. This is usually due to it drying out at the roots. Lack of water would also cause the sod to die and fail.
I would strongly suggest you consult with your local county extension to try to determine what is happening. Based on knowing that, you can determine what needs to be done for it to recover. The following web page has contact information.
In the meantime, here are some general instructions for sod installation and care so you can review the steps taken so far.
I hope this helps you trouble shoot.
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