Not research, the upgrade tab. There should be 3 initial nodes that requires different ores, right? But after prestige all 3 nodes shows require 0 gold, but I can't buy any of them even if I have gold.
Maybe it's just me. It took a while to realize the rebirth button is at upper-right corner. It might be better to 'push' the button left instead of hiding it when upgrade 'drawer' is opened.