While everyone loves the good King Charles today, much of that goodwill is retrospective. The hagiographies by Einhard and Notker, and the plentiful platitudes in the Annals were written after his death, and intended to both burnish the past and reinforce the future. But no one is universally loved, particularly not those who impose their will on others, even with the best of intentions.
In 786, Thuringian nobles launched some sort of a rebellion against Charles and his rule. They were found out, confessed, and punished. And that is the extent of what is known with any certainty. Before we get too deep into an analysis of what might have happened, who might have been involved, and other such questions, let’s take a look at the sources.