@rfindley
I have reproduced the issue described by @nikujaja in both Firefox and Chromium but haven’t identified the cause. (The issue is that audio doesn’t autoplay when lightning mode is enabled.)
Also, when lightning mode is off I noticed that although the audio plays, the audio may actually play twice overlapping if you resubmit an answer after retyping. Sometimes, this is difficult to notice because it may just sound like the audio is louder instead of overlapping. I verified that this issue can be fixed by adding a call to wkRefreshAudio() right before you reset the answer state to allow retyping. I’m still not sure how to fix the original issue of audio not playing, though.
@nikujaja until this gets fixed, as a workaround you could install my fork of the review audio tweak 2 script which should make audio work again. By default, it causes WaniKani to play audio after meaning answers too if you have already gotten the reading right. If you don’t like that, you can change this in settings so that audio plays only when WaniKani would normally play audio.