This is a known bug, likely caused by the JDK:
It looks like JDK issue and is reproducible with a simple scrollable JList.
Sierra generates much more events than El Captain.
These events contain values ~0.1 instead of expected ~1.
But Java converts these small number to 1 anyway.
Edit: see also this OpenJDK bug: https://bugs.openjdk.java.net/browse/JDK-8166591
Edit2: as described in the other answer, JetBrains have fixed their custom JDK. You can download it here and follow these instructions to make IntelliJ use this JDK instead (select the option labeled ... to choose a custom location).