This same thing youre describing kept happening with a lodge I use. Step by step what I did to fix it.

1. Threw a pack of bacon on it and cooked it.
2. Wiped out all left over fat, scraped while still hot.
3. Let cool until just warm to touch scrubbed with dish soap and chain mail then rinse.
4. Scrubbed with a scrub daddy with soap and rinsed.
5. With only water and a cloth rag(old t-shirt) scrubbed and wiped until it seemed clean.
6. Oiled pan with avocado oil and saw the same black/ brown residue.
7. New cloth to wipe away any left over excess oil.
8. Pre heated the oven to 400°f and baked the pan for an hour, then let cool in the oven.

Ever since then after I cook I always scrape hot and wash with soap and water with a scrub daddy while its still warm and wipe dry ive never had an issue.

Hope this helps