Answer: Based on your description, the browned sod you lifted failed to root into the soil and is dead. If allowed to dry out, sod will die very fast.
Sod (and the soil under it) must be kept evenly moist while it establishes. The moisture must soak into the soil where you want the sod to root, it will not root into dry soil. The soil should be damp like a wrung out sponge, not sopping wet and not dried out. Overwatering can cause damage to the sod, as can underwatering.
You might check your watering and make sure it is reaching all areas of the lawn and that it drains the same -- perhaps those areas dried out faster than the rest or were watered less.
You might also check to see if there is some other reason why those spots would have failed such as poor soil preparation or poor sod to soil contact at installation or underground tree roots that steal moisture from the soil or something like that.
If you saw earthworms, they may have been attracted by the decaying organic matter in the dead sod; they would not have damaged the sod.
If the sod originally seemed to "take" and then after a while you saw dead patches, under which you found grubs, then you may have a problem where grubs have eaten the roots. If this is the case, I would suggest you work with your local Penn State county extension to identify the grubs and based on knowing that, treat the lawn accordingly. They may also be able to help you trouble shoot the sod problem.
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