The "official" versions of packages are maintained centrally and many other sites maintain copies. Sometimes, a site may be temporarily out of commission, and sometimes there may be a out-of-bounds condition on the central site's synchronization script, so that it fails to send out correct copies of the whole library to be synchronized.
To go direct to the source (which is generally discouraged, to avoid congestion.
However, today, 2020-03-26 11:15 PDT, the CRAN repository itself seems to be having issues. Try again later.