I bump it too, it’s happening exactly the same for me.
I have been killing mosquitos for around 2 hour in different zones and 0 rewards.
It’s annoying want to create a legendary and be unable to do it for a bug…..
Edit: In Brisban Wildlands-, in the Shattered Henge, it worked for me killing a mosquito there.
Really, good luck with Howler, i hope it wrk for you too. ^^