Hi,
while looking into removing elyxer from Debian I stumpled upon your bugreport.
I just rebuild ngspice with pbuilder without elyxer and can not reproduce
the issue you describe. Either things changed with the current LyX release
(I don't think so, but I did not follow the development closely) or
Package: ngspice
Version: 26-1+b1
Versions of related packages:
elyxer1.2.5-1
lyx 2.1.4-2
lyx-common2.1.4-2
Building ngspice from source fails with the error "No information for
exporting the format HTML.", generated by 'lyx --export html' in the
documentation build stage.