Plant has lost almost all of its leaves from the middle down. Is regrowing now but it does have some leaves with brown spots.
What Are the Brown Spots on My Bougainvillea
Certified GKH Gardening Expert
I do think this a bacterial leaf spot.
There is no real treatment for left spot except preventative care.
That said it would not hurt to treat the plant with Neem Oil. This works as both an insecticide and fungicide.
Here are a few links for you.