This wasn’t happening before but now it is, asked other people and they have the same issue.
Doing a simple
game:GetService("UserInputService").InputBegan:Connect(function(key,this) print(key.KeyCode,this)
end)
shows us that both the I and O keys don’t show up, this could be related to zoom in and out feature, binded to the same buttons, but other roblox system commands don’t share the same problem. This is definitely a bug
Most likely what you stated about the zoom buttons.
This may be because users could easily get stuck in GUI’s while in first person.
How’d I go about fixing this? It wasn’t a problem until recently
then detect the camera zooming out and in 
Can’t tell if you are joking or not, but I’m not using roblox’s base camera
Pretty odd, tried it my self and it does the same or doesn’t print “I” and “O” not even GetMouse() would. All though the keycode enums do exist for them (Enum.KeyCode.O and Enum.KeyCode.I) 
funny enough it works in an older versions, rblx.lua is wild
that’s not a fix either way though
This began happening to me too, just today actually. The i key does not register at all when testing in studio, whereas it does register when in the Roblox player.
An impractical ‘do this alongside this’ bandaid solution for something that shouldn’t be an issue in the first place is NOT how you fix things xd
Yep along with this other post it definitely seems to be a bug especially with input began for the IO keys. @colbert2677, @nin900500 and I are getting the same issue but for context action services for the IO keys definitely seems related.