I was able to claim and use the feldrake and other WoW drops prior.
I went through the available support options under the “common problems” category:
I had not recently changed my twitch or battle.net passwords
I tried multiple browsers → all without extensions.
I have a screenshot on the twitch rewards page showing I claimed the firework 7 days ago.
I got desparate and relinked my battle.net accounts after 5 days, but now 2 days later that didn’t help.
I really love collecting toys and hope there’s some solution!
Claimed mine 18 days ago, got the other rewards but not the firework, yes my account is still linked. Blizzard blames twitch, twitch blames blizzard. Guildie has same problem.