I am having a similar issue. I have ensured that the profile is logged out. When I click the Oauth tool it loads the secondary screen but does not enter a browser and simply tells me to enter the bot login name. There is no manual option for oauth so I can not use the tool. Same problem sourcing OAuth for the Streamer account.
I have closed out of all Twitch profiles, I have given the program admin priveledge and I have ensured it is cleared on all firewalls.