The IP appears in quite a few blacklists, eg
https://www.abuseat.org/lookup.cgi?ip=45.5.69.238. We use a combination of lists to prevent forum spam, unfortunately this is done at the network level so it does also block Twitch auth. We'll look into ways to prevent that. I've removed the block for now, but it may come back on the next list update, however once you've connected your Twitch account it should only need to communicate with Twitch in the future.