Do you have any custom CSS / theme enabled, or a browser extension that might be blocking the icon?
I don't see any restrictions on your account, and I'm fairly certain that it's not possible to block downvotes like that. Nonetheless I'll pass this along to the rest of the team to check if anyone knows anything.
We can take action if someone is abusing the downvotes (ex. Following someone around and down voting everything they post), but we do that by banning the account. Those actions will be listed in the modlog. See here: https://piefed.ca/modlog?mod_action=&suspect_user_name=Ofiuco%40piefed.ca&communities=&user_name=&submit=Search
Looking at our dashboard, I don't see any unusual voting activity on your account that would justify admin action.