The temporary fix for the YouTube addon is to install the Alpha release from Github. Alpha1 is for Kodi Matrix. Alpha3 is for Kodi Nexus (20.1). Make sure you install the correct one! Then go into YouTube Settings and turn off MPEG-DASH. If you don't turn off MPEG-DASH, the video may freeze and crash YouTube. Here's a link for the Alpha releases:
This is a temporary fix until the developers release an update. This also limits resolution to 720p.