No need to apologize, almost everyone here has had the same or very similar situation happen to them.
When you’re placed in AP, it very much appears that Montreal does a SAO (Security Advisory Opinion) which is essentially what 5535 is.
Montreal has a reputation for doing this more than almost any other consulate in the world, and nobody knows exactly why. There have been theories, but honestly the thing that makes the most sense to me is that Canada is very easy to immigrate to. There are people that move to Canada just to be closer to America.
Basically whenever you’re placed in AP at Montreal, there are two “pathways” your AP goes. One is with your consular officer, keeping note of your case and what they need to follow up on. The other is DOS background check.
This seems to have been the cause of everyone’s issues, and became very obvious when the Afghanistan withdrawal took over as priority #1 over any other background check. Thousands of visas put into a pile that wasn’t moving, and then 1-2 years of cases backed up by putting them all into the “we’ll do this after the background check” pile.
In this group the wait time varies from 4 months to over a year. Most of the movement has been due to lawsuits, with the occasional organic case movement.
Obviously it’s up to you, but if you want to have this resolved in the next few months, I would recommend filing a lawsuit if you can.
A lawsuit guarantees something will happen, waiting could be another year.
I’m very pro-lawsuit after experiencing it here, in DV, and in multiple visa categories. The most happy people are the ones that file a lawsuit and almost everyone wishes they did it earlier.