[0]: https://web.archive.org/web/20200229123317/https://twitter.c...
[1]: https://web.archive.org/web/20200229164715/https://www.cdc.g...
I think it's possible they deleted old content to make sure invalid data isn't out there on the web to be cached, linked to, quoted, etc.
However, if they really are lying now (i.e. making current statements) saying that they never flip flopped, then yeah that would be weird.
You don't want people linking to obsolete information under the surgeon general's twitter. There is no way to flag a tweet as "for history only ignore the actual advice as what to follow." Meanwhile, the old "don't mask" mandates are in the CDC's website in their archives, which are purposefully hard to find (for similar reasons, to ensure you know you are going to historical and not current publications).