PO 7.5 Message Monitor Cancelled Message Count Inconsistency

Hi,

In the NWA->SOA->Monitoring->Message Monitor there is often 1 or 0 cancelled messages. This number decreases over time. For example 5 minutes ago the number shown in the image was 1, now it is 0.

However when I click on the number there are more cancelled messages.

What can be the reason for this?

Thank you in advance.