Additionally some settle operations get "Operation Change Target INVALID" statuses now, whatever that means (on both the default and a custom behavior tree). It's stopping them from settling is all I know.
I can confirm the default (sans AI+) behavior is not settling as much. I tested this by giving each AI 4 starting settlers on Deity, and by turn 109 several AI's still had not planted all their settlers yet even though they had good riverside starting spots available nearby; the settlers would just shuffle around endlessly.
Also, another possible issue was discovered by Isau in his "Quo's Combined Tweaks", here, which states the following (in reference to the new Summer patch):
From Isau: "This small update attempts to correct a possible bug on Firaxis' part that is resulting in civs being too ready to move from neutral to friendly and to formally declare friendships.
- Changed min threshold for a Civ to declare friendship to 15 (up from 5)
- Changed min threshold for a Civ to flip from neutral to friendly to 5 (up from -5)"