Certain nations Upstream Trade Propagation propagates too hard.
e.g. Spain sticks 100 light ships in Sevilla. Gets 400 base trade power, x2 for +100% trade power modifier (probably slightly lower in-game but I'll round it up), so 800 trade power. Then every upstream trade node gives 20% of the downstream trade power, meaning 5 more trade nodes get 800 x 20% propagation x 2 trade power modifier = 320 more trade power in 5 nodes, for a total of 2400 trade power so far. Then that propagates again for 128 trade power in the next level to about 15 more nodes (4320 trade power total now). Then you realize that a single node can be upstream more than once (e.g. Ivory Coast is upstream of Sevilla, Caribbean, and Brazil and therefore gets something like 550 bonus trade power) and the benefits are getting out of control. And we haven't even considered that spain might actually have colonies and control CoTs and such. With just 100 light ships Spain is swamping the provincial trade power of dozens of trade nodes, most essentially the New World and Africa who are far, far behind in trade efficiency and trade building boosts.
I'm unsure of exactly what has changed in AoW such that I now see AI Spain and Portugal with thousands of trade power in their home node and nearly thousands propagating into Caribbean and other nearby nodes. I think it may simply be that the overall income increase gets the AI to build far more light ships, which leads to a domino effect as they can then suck up more of the improved AoW trade value and build even more ships.