I'm not sure how much this matters because it's mostly a backward compatibility issue with something which is a relatively new feature anyway, but
(asdf:output-file[s] 'asdf:monolithic-fasl-op ...)
no longer works in 3.1.3 (at least on CCL/Linux). The new nomenclature is apparently:
(asdf:output-file[s] 'asdf:monolithic-compile-bundle-op ...)
is 'asdf:monolithic-compile-bundle-op indeed the exact replacement for 'asdf:monolithic-fasl-op?
FWIW, (asdf:operate 'asdf:monolithic-fasl-op ...) still appears to work.
I apologize for not running tests on my own stuff before the release of 3.1.3; I'll try to make a point of doing that for future releases.