Hello! Sorry for the delayed reply. I'm so glad you're enjoying using Item Flood~!
Hm... I'm not sure exactly. To catch the Twitch redeems, I use something called PubSub through a library called TwitchLib. I'm not sure if this is an issue on Twitch's end, or with the library I'm using, but we have seen this happen before and I think it happens with other programs that use PubSub to track redeems. I'm definitely going to do a deeper look into all the logic when I do the next update (though I don't have an ETA for that).
Sorry I don't have a better answer for you! But I am definitely aware of it and hope I can find a reasonable solution for the next version.