The trouble here is with the umlaut symbol `ü` in folder names. It seems GTR2 was programmed long time ago as ANSI program, therefore it does not work properly with language-specific symbols in filepath.
Mod version: EEC_GT3_MOD_GTR2_V2_32.7z
`2012 ADAC Mühlner Motorsport` and `2012 ADAC Schütz Motorsport` are absent in GTR2 if Windows locale set to English (or whatever else language without `ü` in its ANSI char table).
The bug was observed at this race
, Mühlner Motorsport car was rendered as the placeholder Pace car, as an absent content or mod not installed.
Workaroud: set Windows locale as German.
Possible fix: rename team folder names in the mod as `2012 ADAC Muhlner Motorsport` and `2012 ADAC Schutz Motorsport`.