Mod: 'German Football League System' by D4n1v4l on Steam. All Daveincid realism mods enabled.
Affected leagues: German lower leagues that are not in the vanilla game. In other words: 4th, 5th and 6th tier. Had the same problem with a Serie D database.
Bug: Sponsorship in lower leagues is too high, which causes all clubs in these leagues to turn pro. In reality, most of these clubs are semi-pro. When I ran the first season again as a test without the sponsorship mod added, the sponsorship incomes were €0, which is also not realistic.
Further comments: Again, I don't necessarily think this is a bug, because I added your mods to another lower league database, but I still wanted to let you know!