Okay, I have a theory. I looked back at the trailer releases for The Last Knight. The first teaser was released on December 5th, 2016 (which was about 6 months before the movie). However, they released a short IMAX featurette for the Last Knight on November 16th with Fantastic Beasts, which was 7 months before the movie. At the time a lot of people thought it was going to be a trailer, and were disappointed when it was just a BTS reel (mostly with clips from the previous movies). My theory? This is what's happening now. At some point during this week or next, Paramount will release a BTS reel to go with Solo. We're at the exact same point now that we were when the BTS reel was released for TLK, it's just a different time of year since Bumblebee releases in December. Of course this could be completely wrong, but it would make sense. The full trailer could hit next month, or even the month after.