the different nutrients may not have completely agreed with each other. Nute companies design their nutes to work with their own lines so who knows what sort of potential chemical reactions could take place when changing to a different company or nute line within the same company. That being said possibly the only thing you could have done differently was to give them a good flush before changing over the nutes. I don't know how much difference it would have made without a flush, if there were major problems there would have been nutrient lockout or other viswible signs.
As for bud size, there's so many varying factors, light, air, nutes, strain, defol/no defol, plant training, temps, RH, pH etc. They're good looking buds you've got there, as long as you get the desired effects, bud size, density and yield can be worked towards in future grows.
I'll be posting some day 49 pics of my current auto grow journal in a couple of hours if you wanted to do a bit of a comparison. I changed from transition to bloom nutes two weeks ago. Buds everywhere.