I just opened a new Line of Credit account with Northwest Federal Credit Union (NWFCU). It isn't appearing in Mint even though it shows up when I log in to my bank.
Update: this morning, it appeared.
All of my other accounts are appearing. I ran in to a problem like this with Fidelity, and ended up having to add a new account for Fidelity in Mint each time, and then mark all of the existing accounts that are already being downloaded as duplicate accounts, so that I only get the new account downloaded.
This is a really ugly approach, and I was hoping that it only applied to Fidelity accounts.