BUG Type 2
This deduction assumes the puzzle has exactly one solution and that all earlier candidate removals were sound. BUG Type 2 uses two or more exception cells carrying the same guardian digit. After removing every guardian occurrence hypothetically, the complete remaining state must satisfy the BUG counts.
What is BUG Type 2?
The exception-cell count is not fixed at two by the logic. Verify that all other unsolved cells are bivalue and that the hypothetical removal of the shared guardian digit leaves the required twice-per-sector BUG occurrence structure.
Type 2 has two or more exception cells carrying the same guardian digit. Removing every guardian occurrence hypothetically must restore the verified BUG structure. At least one exception cell therefore uses the guardian, so the digit can be removed from a target that sees every exception-cell occurrence.
How to spot it
Find all exception cells carrying one prospective guardian digit and verify the whole candidate state after its hypothetical removal. A target for that digit is valid only when it sees every exception-cell occurrence that could supply the guardian.
The logic
If no exception cell used the guardian digit, the excluded BUG state would remain. Under the unique-solution assumption, at least one exception cell must use it. A target that sees every possible guardian occurrence cannot use the same digit and can be removed.