I appreciate all of the help. I calibrated my hydrometer (mine is calibrated at 68F per the packaging) after purchasing a new hydrometer. I also used this hydrometer on my last batch so I’m confident in my readings.
I know many (such as brew_cat) might not appreciate my decision, but I’ve already moved on. The batch is still sitting in the carboy, but I’m not going to bottle it. I’ve already ordered a new grain bill for a new batch.
I’m confident in my post-mortem. Will I really know what happened? No, but all of the evidence and facts point to one of two things - the yeast or a conversion issue (the latter more likely in my opinion). Did I learn anything out of this? Yes. Despite the comments, I learned a lot with this batch; how to build a recipe; how to calculate IBU, SRM, etc; about grain mill settings; the importance of a starter for high gravity beers; how to test mash conversion; how to mash in a BIAB and equipment requirements; more on temperature control; what is a first wort hops; how to harvest yeast; the difference between a stuck fermentation and one that is finished due to inadequate conversion; and how to test for conversion. All of this will help in my future brews.
I started this to have fun. I’m not going to spend an enormous amount of time worrying about this batch, etc. That’s not fun in my definition. I’ll take my lessons learned, move on, and start the next batch.