Just in case anyone else has a similar setup to me (Intel NUC 7i5BNH running Windows 10) I had to change some audio output settings to get Dolby Digital/DTS passthrough to work properly after the upgrade to Kodi 19.
With v18, I was using DirectSound as my audio output device, with 'Number of channels' as 7.1. In v19, DirectSound doesn't seem to work at all (I just get silence for the first 20 seconds of playback, and then the playback gets 'stuck' there) so I switched to WASAPI which sort of worked, but I was still getting intermittent dropouts with DD & DTS tracks, for a second or two every minute. After a lot of googling, I found someone on some other message board complaining of a similar issue and said that switching the 'Number of channels' to 5.1 seems to remedy the problem.
I haven't done extensive testing, but this seems to have worked for me and pass-through is working properly, even with Atmos content, which is obviously greater than 5.1 channels.