Hi there
This is prime time for a developmental leap, a language leap comes at around 21 months (so perhaps your LO does these things just a little later as they are all different?) which can totally throw off sleep. I remember having a thread myself at that age wondering what had suddenly gone wrong with my DS's sleep. In your case it could be a combination of transitioning to the BBB as well or that could be just coincidence.
Usually the development just passes and sleep goes back to normal after a couple of weeks. Many people ride it out. When mine was taking so long to go to sleep at night I chose to shift BT later so that we basically cut out a lot of the fussing and call backs.
Your LO has a good long nap and also a good length night, there is a chance he is UT too but it may not be long term, it might be just during this leap and you might find in another week or two the routine has returned and your LO is suddenly saying a lot more words than before.
Hope that helps