Whether masks could be effective was never in debate. If you recall, they were concerned people would use the masks incorrectly and that could do more harm, as well as potential shortages in the supply chain and getting the masks to the most important workers. I don’t recall the CDC ever saying “masks do not work”

Fauchi, presumed spokesman for the CDC, came as close as possible to saying so, and/or was taken as such.

If that early statement can be justified by "fog of war" changing virus-related information at that time, then Fauchi should have allowed himself that complication. By offering "there were not enough masks available then" as a later explanation, he seems to have explained it essentially by saying he lied. In doing so he apparently threw away a substantial amount of his credibility, for many people. At worst a lying move; at best a lightweight move with lives at risk.

I don't think the CDC made a mistake - I think they intentionally "lied" for the sake of the public good, aka the Noble Lie.

Rather than saying "Hey lets hold off on buying masks so that we have enough for essential care workers" they instead said "do not buy masks because they aren't effective, or might even make risk of infection higher!"