I don't know if you managed to solve your issue but I recently installed Opera GX and ran into the same issue you have.
I removed the Twitch bookmark (which I had imported from another browser), then saved it again to Speed Dial which left me with two links to Twitch on the Speed Dial tab (one of which was already there when I first opened Opera GX).
Finally, I moved the Speed Dial link (the one I just saved) to my Bookmarks and it was fixed.
Hope this helps you!