Illuminated Cloud seems to be breaking something about the Change Signature refactor in Java projects when it is enabled. If I disable IC, this problem goes away. The issue is that the Refactor and Preview buttons don’t do anything when clicked.
Nothing is appended to idea.log and no error shows anywhere else from the time IDEA finishes startup through reproducing this issue. JetBrains support took a look at this already and suggested I file an issue with Illuminated Cloud.
IntelliJ IDEA 2020.1.2 (Ultimate Edition)
Build #IU-201.7846.76, built on May 31, 2020
Runtime version: 11.0.7+10-b765.53 x86_64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.