the SMAA implementation got broken from engine postprocess changes in 4.15 and sadly the guy that ported it to UE4 isn’t maintaining it anymore. So far no one has reported a way to get it working (I tried myself using the guy’s suggestions but just failed). And with the changes in the postprocessing from 4.17 I’d expect it to be even more broken now 
Other alternatives: proper TemporalAA. Epic “got married” to the temporal AA technique not just as an antialiasing tech but also to make other rendering features more affordable (i.e. temporality of DFAO, dithering+temporality in SSAO) or to even achieve some things that just look horribe without TemporalAA (smooth mesh blending via PDO and dither alpha, fake translucency via dither alpha).
With this in mind I don’t think it’s unreasonable to expect TemporalAA to achieve a better quality but sadly it’s been pretty much the same for about the last 7 major releases now.
I’ve seen TemporalAA perform quite well in all recent Ubisoft games (and not so recent, basically since Assassin’s Creed Unity). However I’m not 100% convinced that they use TemporalAA alone or if they combine it with some other AA technique (it’s explained in a paper IIRC, but nothing stops Epic from mixing AA techniques). I’ve also heard the new Doom’s TemporalAA looks great but I haven’t tried it myself.
I know a certain guy might barge in and say all engines are different etc, but in the end it boils down to Epic focusing their efforts on something else than more/better AA options.
also maybe SMAA officially supported
interesting. I don’t suppose any of this is exposed in the UE4 editor right? (in UDK you could at least select the preset). I guess it’s time to play around with the usf (and play shader compilation simulator 
)
the reason you get artifacts on “indirect lighting” is that DFAO works over multiple frames independently of your Antialiasing option. in other words they are completely unrelated to the antialiasing technique, it’s just that TemporalAA helps to soften them out, because, well because that’s what TemporalAA is designed for (softening out temporal artifacts)
anyway you solved it for your use case, you solved it on a relatively simple scene (you have textured meshes but they are all big and solid, no foliage/grass which means quite more irregular sharp shapes/edges, no small/far objects causing sub-pixel artifacts, etc) and you solved it by using FXAA which isn’t an effective solution for all projects.