This is still happening even in the latest forge for 1.15.1. it's really annoying because at times it completely breaks the game...Mobs attack retardedly and they aren't really a challenge anymore which is game-breaking.
seems the admins deleted my original post that was linked here, they must REALLY want to break support for 1.7. so here's the cliffnotes.
- In your build.gradle replace "jcenter()" with "mavenCentral()"
- in ./gradle/wrapper/gradle-wrapper.properties change the "gradle-2.0-bin.zip" to "gradle-2.6-bin.zip"
- do your usual workspace setup again: "gradlew setupDecompWorkspace --refresh-dependencies idea" be sure you don't use powershell, that has it's own issues, cmd/terminal do the job just fine.
This fix should also fix intellij 2019 compatibility.