Discrepancies sending metrics to 2 servers

We have an intranet website for which we are sending metrics, via addTracker, to two different Matomo instances on different servers.

What’s strange is that when comparing monthly metrics, one day at a time, the number of Users matches between servers, however, # Visits and # Unique Visitors do not match. The difference is small - 1% or less, however, I don’t understand what is happening, not understand how I can debug to help me figure this out.

Any ideas or suggestions?

Thanks!