If the CDC did the opposite in each of these cases, people would find fault in that. "They told the general public to wear masks early on, leading to mask shortages at hospitals!" And "When blood clots were reported in JnJ vaccine they did nothing to protect Americans!"
False dichotomy. The CDC's only two choices weren't to say "everyone wear masks" or "masks don't work." They also could have told the whole truth and said "masks do work, but please hold off on wearing them until we're sure there's enough for first responders."
If they only had the choice to do one of two diametric opposite actions you might have a point. Of course, in reality, there is no such limitation. If the CDC had told the public masks work and research shows home made, cotton, or surgical masks are significantly better than nothing and we need to get our N95's to our medical frontline... Or, you know, been prepared with enough masks for medical frontline people. Doing nothing when blood clots were reported is a bad idea, doing analysis (ideally in advance) to know what levels of side effects should and shouldn't be cause for alarm would be a better idea.