Select Layer 1, your problem nested comp, in the Project Panel and embed a screenshot showing the properties of the comp. Also, show us all the modified properties of the layer by pressing the 'u' key twice. This will reveal everything that is changed.
What version of AE are you running. I just tried a pre-composed 3-hour comp, the maximum length for an AE comp, and you can still slide the nested comp anywhere you like in the main comp.
Thanks for the trouble shooting tips. I managed to fix it by copying the comp onto a new layer and deletiung the old layer. But if it happens again I'll follow the tips to investigte it. The Version i was using was CC 18.4.1 (Build 4).