Hi @infragrupopardini - that definitely looks odd. If the issue is still occurring, make sure you are on the latest version of the Synthetic Monitoring plugin (Synthetic Monitoring > Settings > scroll down to the bottom of that page to find version. Currently, that should be version 1.12.1.
If the plugin is up to date and the average total trace time values still have discrepancies, please open a ticket with the support team from your account portal so they can further review.