Since updating to 3.5.3, the Meter for Channel A on my Z2 will sometimes not work when using Traktor. Closing and re-opening Traktor fixes the issue.
The meter works fine when using vinyl, so it is definitely a software issue.
To expand on this, I figured out that it only happens if I load my first track into deck A after opening Traktor. If I start with decks b, c, or d, everything works fine.