In some cases, especially on a high traffic website, Matomo may show visits that have no pageviews or other actions listed, and the Visits log entry says “0 action”, and the Real-time report shows no actions for this visit.
If you experience this issue, it is likely because several Tracking API requests are sent and received at around the same time by the Matomo Tracking API server, and these concurrent requests somehow execute at the same time, and each of them may create a Visit. This is not expected but it can occur in edge cases. If you experience this issue regularly, you can reduce drastically how often these empty visit are generated by installing a new plugin: QueuedTracking.
If you’re able to install and setup QueuedTracking then all requests for a given visitors will be queued and executed in a batch, likely resolving the issue.