Re:A comment on Hacker News led to 4½ new Unicode characters...
by dwild on Wednesday December 04, 2019 @01:21PM
(#21705171)
As the article mentions, the O was already in the unicode, it's definition was just updated, thus your font does already include it, while the I is a new symbol, and is too recent to be in your font and thus shown.
http://imgur.com/a/Q2isAPT