Your MCAP file writes clean. Validator passes. Message count matches. You open it in a viewer and nothing plays - https:// hubs.ly/Q04yhwWf0 That's hand-authored MCAP: the worst bugs stay silent until playback. * written as JSON → every topic
Hand-authored MCAP files hide bugs until playback
A Voxel51 post warns that hand-authored MCAP can pass validation with matching message counts yet fail to play, since the worst bugs stay silent until playback.