Every time I change my avatar it won't change in game. I also noticed that it changes back to my original avatar that I had previously, making it feel like it didn't change at all.

Is this a bug or issue with the forums and the game, because I've tried changing my avatar for the past week and am unable to because of this.
Someone please give me insight.

It's a possible bug. Have you tried to click "remove avatar" first? And after that check in game. If there's no profile picture then you can put the one you want, will work for sure.

No, it doesn't work. It technically works, but then it doesn't.
I removed the avatar on forums and then I log into TFM and the avatar is gone, but then I change it and log in again, it goes back to my original one that I've had on my account for years.

When I changed it on forums it'll remain changed for a couple of hours or so and then revert back to the original one I had. But when I delete it, it seems to remain deleted. although, I didn't test this out long term, just for this brief moment to see if my avatar would change.

I'm also not sure if this only on my side, because when I did change it, someone did comment on my profile picture in-game despite me not being able to see it changed on my side. This seems like a communication bug between servers, but whatever. If there's any other suggestions or insights, I'm willing to try, if not, I'll have to delete my avatar and hopefully it'll stay deleted. Sad, I can't change it. I've had the same avatar since 2015 and I wanted to change it since I came back playing TFM again.

try removing your avatar, deleting your browser cache and uploading the new one

the same thing is happening to me, even with deleting cache. removing my avatar does work, but when I upload the new one + clear cache the old one is right back.