I found two things:
1.
Johann = short form of Johann(es
Baptist or Evangelist/a)
SEIBICKE,
Wilfried: Historisches Deutsches Vornamenbuch, 1996ff.
2.
Johann […] It was a fashion in the 17./18 century to combine
Johann with a second forename, which was the actual first name:
Johann Sebastian Bach […],
Johann Gottfried Herder […],
Johann Wolfgang Goethe […]
KOHLHEIM,
Rosa und
Volker: Das große Vornamenlexikon, Mannheim 2003
Hope this helps.
Andy ;—)