Hussites or Herrnhuter Brethren. Check out the Moravian Church on Wikipedia. They were an early Protestant sect that grew up in Czech areas that had Orthodox roots. There was some resentment against Catholicism that led them to reject Rome a century before Luther.
Neither the Moravians, nor the Hussites nor Herrnhuter had Orthodox roots. That is a relatively recent revisionist idea put forward by some Orthodox - especially the Czech Orthodox Church which is deperately trying to create a history since it practically lacks one.
Jerome of Prague is often held up as if he were a convert to Eastern Orthodoxy - yet his “conversion” went unnoted by everyone in his day including by Jerome himself. Not even his enemies, such as John-Jerome of Prague, ever mentioned it.