Product: Lightroom 6 (not CC) on Windows 7 64-Bit
Bug. Attempting to start LR6 with a DISABLED network connection results in a hang that does not clear even after reboot. The only solution I've found is to remove a .slc from C:\Program Files (x86)\Common Files\Adobe\SLCache. This forces re-registration of the product.
The desired behaviour should be the same as removing the network cable. This lets LR6 carry on working without a internet connection.