There's the Dogon issue (by Jim O)...
But apparently, all writings from -150 BC to 980 AD state that Sirius was RED! As brilliant as it is now, but red (like Aldebaran, Antares or Betelgeuse)!
This seems impossible if we know how stars evolve, as Sirius is now a white-blue star.
How come?
Is it because the star is so low above the horizon? That's not the case everywhere!
Did Sirius B turn nova? Sirius B is a white dwarf: it couldn't have changed from a red giant to a white dwarf in less than a million years. Sirius A doesn't expell enough matter for Sirius B (8 to 32 AU from A) to turn nova. B would have to shine 10,000 times more for it to be noticeable.
B being less massive should normally evolve much more slowly than A. It thus could not have reached the white dwarf state before A, unless it was captured.
Herschel suggested a cloud of dust matter reddened A, but there was no reducing of the brilliance and where is that cloud?
A team of astronomers (with Bonnet-Bidaud) has been hunting for Sirius C (which would explain a transfer of matter leaving C and reddening A when C was very close to A). C's orbit would be very excentic and last 2,000 years.
Problem: C has not been found and the team concluded it doesn't exist, not even as an exoplanet.

Sirius may be the shiniest star in the northern hemisphere, but it still is....mysterious.