What's even more worrying is that there's nothing in the logs! And no prompt at all. After rebooting the phone I see a prompt just once, but it never appears again no matter what I do (killing ES File Explorer or/and wiping its cache).
Can you please look into that?
I have a Nexus 5 phone with stock Android 4.4.4 (rooted via TowelRoot).
Edit: There are people who experience the same problem.