Horse related stuff... drives me nuts and makes me shout at the telly.
These days anything period appears to require Friesians, and whilst they are a very old breed, and were brought to many countries.. the idea that EVERY knight, princess, prince etc rode one and every carriage was pulled by one since the year dot is absolutely laughable. In fact very few were ridden early on, the big flashy ones were carriage horses, not riding horses.
In many of the time periods these things are set in, we'd have had an abundance of popular breeds - flashy welsh ponies, even flashier lighter hackney horses and ponies, chunky working cobs.. they'd have all been far more available than the Friesian.
Then theres the tack - so much of it is BLACK.. black leather work is for the working animal, carriage horses, farm horses - BROWN leather is for riding horses.
Its also often shown as being very chunky crude stuff - in fact fancy tack for the posh ridden animal was very very fine (Sewn at 16 stitches to the inch, you'll struggle to get that now as the pricking irons used to mark the stitches are either antiques or made to order!).
Or its just plain wrong, nosebands and bits and saddles that just didn't exist!
Argh!