Do you think it's wrong that Bridge-"br-data"-MLAG shows an empty value in the "Active Role" field for the primary switch, state: connected. For the secondary switch, it says: Active role: secondary.
terminal: /interface/bridge/monitor br-data
it correctly says:
mlag-state: connected
mlag-active-role: primary
MLAG seems to be working properly.
Does anyone else's winbox in MLAG show Active role: primary or is primary also empty in your configuration?