I think in the case of masks, it is highly plausible there was no deliberate attempt to mislead.
While at the time it seemed pretty clear to me that masks had a high probability of being helpful, there was a dearth of research that would support this conclusion - indeed the very limited research conducted on public mask usage did not seem to support it.
On top of this, I believe a major contributing factor was that many medical experts were used to very stringent mask protocols, and did not seem to consider the obvious differences between a hospital setting (where Covid may be rife) and every day life where it is a medium-to-low risk event, and carried over their belief that anything less than their stringent (and unrealistic protocols for the public) would render them useless.
I saw many regular doctors expressing this belief on Twitter at the time, as well as explaining how mask fitting was a laborious process, and that without this the mask would be useless, or that if you touched the mask while taking it on or off it would be worse than useless.
So, I think it is entirely possible that experts were giving leaders and journalists their honest assessment that masks were useless for the public - no doubt more exuberantly than they would have done if masks were plentiful, but not necessarily dishonestly.
I don't disagree that public messaging is highly manipulated in general, but I think it is more plausible that this particular case was fabricated by flaws in the decision process rather than dishonesty.