It looks like there is one from the current list (the one the post is about) which this list dates back to December 2020.
Not sure if they get removed from the list ever? Will have to dig a bit more to find the old lists.
Looks like the previous two were Badminton 2018, and then Blair Castle 4 months later in 2018.
This article is from 2014 and mentions some verbal warnings; https://e-venting.co.uk/2014/06/mary-kings-yellow-card-at-bramham/
If you compare this to Oliver Townend who has recently received two verbal warnings within the space of a month for Badminton and for Tattersalls. It appears that Oliver Townend at Tattersalls was given a verbal warning because he apologised and then afterwards made every effort to find out how the unmonitored child who was in the middle of the galloping lane was when he got off his horse. The ground jury accepted that he had slowed down as requested to do by the official but not enough care was taken. The Badminton verbal warning for abuse of the horse with whip and spurs. Though Oliver Townend admitted on Badminton radio that the horse was lighter in weight than he had wanted and this might have impacted on the horses energy levels at the end.
Just doing some googling I never heard about HMs horse getting stuck on a jump and getting a red card. Poor horse.
https://equusmagazine.com/blog-equus/good-news-bad-news-from-uks-burghley-horse-trials/