Why is there continuity between hot and neutral in the unmodified part of my circuit?
Not only the possible continuity from a lamp being the issue but if any of the switches are lighted can also be the source.
Last and most common is a plugged in transformers on the same circuit Will look like a dead short. This messes with new apprentices every time.
A transformer Looks like a short to a continuity or DC ohm meter test but AC has a reactance so it is not actually a short.