> Maybe old JVM parameters have persisted in settings somewhere?
This is an annoying behavior on at least Intellij Idea (I don't know about other Intellij products). If you ever increased its memory limit (it's an option on one of the top-level menus, and it will also occasionally suggest increasing it if it ever notices it's using too much memory), it copies the idea64.vmoptions file which contains not only the memory limit (-Xmx), but all the JVM parameters, from the binary directory to your configuration directory, and so the JVM parameters on it will be kept forever, instead of being changed when you update the IDE. The fix is easy: find that copied idea64.vmoptions file, write down the memory limit on it, remove that file, restart the IDE, and go to that top-level menu option to set the limit again. This will copy an updated set of VM options to your configuration directory.
This is an annoying behavior on at least Intellij Idea (I don't know about other Intellij products). If you ever increased its memory limit (it's an option on one of the top-level menus, and it will also occasionally suggest increasing it if it ever notices it's using too much memory), it copies the idea64.vmoptions file which contains not only the memory limit (-Xmx), but all the JVM parameters, from the binary directory to your configuration directory, and so the JVM parameters on it will be kept forever, instead of being changed when you update the IDE. The fix is easy: find that copied idea64.vmoptions file, write down the memory limit on it, remove that file, restart the IDE, and go to that top-level menu option to set the limit again. This will copy an updated set of VM options to your configuration directory.