Back when Usenet was still functional, de.sci.history (German history group) had some dedicated proponents of a German conspiracy theory that the early middle ages (Carolingian dynasty in middle Europe) didn't exist. Basically their argument was that there are gaps in the respective documents and also a lot of forgeries, and the best explanation was that a few hundred years were missing. This of course ignored all the carbon dating, and as well as the parallel chronology of other cultures (including early Islam, which fell exactly into the "missing" period)
Ah I [vaguely] remember something about a large gap in German history where no one got a diploma. The argument was that forging lists of names and attributing credentials to them without works or publications was very complicated.
If I remember correctly, it was the same period for which Morozov demonstrated the astronomical records to be way off.
https://en.wikipedia.org/wiki/Phantom_time_hypothesis
At the beginning I found it amusing, but after some time it got just tiring.