Suddenly all JS Files concatinated in development

Hi all,
I encounter a strange problem in my Rails 5 project. Suddenly all JS-Files are concatinated (but not minified) to one debug-application-xxxxx file.
Before when worling in development environment all js files were seperate files being loaded seperate. This is really mad when debugging JS Code
I tried the obvious config settings for the asset pipline but no luck so far. Any suggestions what else I can try?

Best Regards
Andreas