Karabiner Elements: Why is a series (or sequence/batch) of keys called in {…"to": …} only executed every second time?
I think your workaround perfectly demonstrates the reason: you are selecting "Element information" via the GUI, and the context menu may take a few milliseconds to be brought up. This isn't an issue with Karabiner specifically — if the E and return keycodes are sent instantaneously after right-clicking, the context menu may not be in focus yet, and they won't be directed appropriately.

In short, if you're making a GUI macro, you may need to wait for the GUI to respond.

As I see it, there are three possible solutions:


simply add a brief delay, as you've done,
use an alternate tool (e.g. Keyboard Maestro) which allows you to pause until a certain condition is filled, or
use an alternate method of activating the desired outcome, i.e. something which doesn't rely on the graphical user interface at the user level, such as AppleScript (though I don't know if such an option exists for this specific goal).