I also had this issue. My first fix was using the "--refresh-dependencies" gradle arg. Worked every time but really slowed down build time as it has to redownload the deps each time.
Today I tried totally re-installing forge gradle by just deleting the .gradle folder in my user area (beware downloads take ages). This seems to have fixed the issue but I've only run 5 test builds so far.
"gradlew build" fails on task ":reobf" with IllegalArgumentException
in ForgeGradle
Posted
I also had this issue. My first fix was using the "--refresh-dependencies" gradle arg. Worked every time but really slowed down build time as it has to redownload the deps each time.
Today I tried totally re-installing forge gradle by just deleting the .gradle folder in my user area (beware downloads take ages). This seems to have fixed the issue but I've only run 5 test builds so far.