As a follow up to this post, I just noticed another inconsistency. I checked my twitch drops to make sure they were still there, and according to twitch I have the following:
GamerZahk, Zerator, JdG, Lomadiah, Burke Black, TheSpiffingBrit, Quill18, Lewis, and Marbozir.

Yesterday, when selecting the avatars to play against, only the defaults and Quill18, Lewis, and Marbozir were available (and now none are). Very strange. Also [Dev] Default Personalities 1&2

I seem to have the same issue. Yesterday, when I was playing, I had Yogscast Lewis and Spiffing Brit unlocked. Today, when I launched the game they were no longer unlocked. I've tried resynching my Twitch and Steam accounts with G2G, disconnected and relogged my G2G account in Steam and such - but no luck so far, sadly.

I am still missing my Creator Avartars. I have just one, okay is not that much, but i redeem the drop, but no avartar in-game or as content here.

I followed the instructions here: https://support.sega.co.uk/hc/en-gb/articles/4405785648401-Known-Issues#text at the top since I had played in the open devs, and it got rid of the dev personalities (and my saves and my own avatar but w/e). Relinked my g2g account in game, still no avatars. They don't show up in my list of personas on g2g either, but they're definitely still on twitch. Resynced my twitch account on g2g, no luck.

If you go to the menu option for twitch drops under humankind of g2g, the instructions state that once you get the drop, it'll unlock a badge on g2g, which will become a persona. I definitely don't see those badges on g2g, locked or unlocked.

On first launch of the game I didn't have any of my twitch drops and my avatar wouldn't save. I closed the game and checked my file integrity and that fixed it. 

Then I started a game earlier myself and saved after a few turns as I had work. Just jumped on again and noticed the AI persona avatar had changed, I went to the main menu and they were all gone, furthermore they're not on my Games2gether and it doesn't even show the list of unlocked/locked avatars on the twitch drop page of G2G. I just checked integrity again and it didn't work.

I had all but two of them in game just fine yesterday, today they are all missing. This is also likely the culprit behind opponent avatars getting shuffled in save games.

This issue seems very intermittent, I restarted my game earlier and there were the three I had before (Lewis, Marbozir, and Quill18) available, but not the rest of the drops. And then after I restarted my game again they went away again, and once more were replaced with random avatars in my save game.

One more update: i took a second look at the twitch drops page on G2G and it does say that I have unlocked the three avatars that I've mentioned as sometimes being able to access, but it claims that the others (that twitch says I do have) are locked.