Could it be something related to /boot/retpoline-4.15.0-20-generic? It's 0 bytes, the retpoline-4.15.0-13-generic is 17kb.
Could it be something related to /boot/retpoline -4.15.0- 20-generic? It's 0 bytes, the retpoline- 4.15.0- 13-generic is 17kb.