recently I used the conversion tool to convert 5 AP's to LWAP. 3 were in one building/subnet and 2 were in 2 different buildings/subnets. The conversion tool said everything worked but when the ap's rebooted only one out of 5 actually connected to the controller. I had to go touch the other 4 and tell them the ip of the controller.
the one that came up was part of the 3 that lived in the same subnet.
I have DHCP setup across all scopes with option 43 and one of the controllers set as a master.