Explanation
Deconflicting with the penetration tester is the best thing to do next after the security alarms are triggered during a penetration test, as it will help determine whether the alarm was caused by the tester's activity or by an actual threat. Deconflicting is the process of communicating and coordinating with other parties involved in a penetration testing engagement, such as security teams, network administrators, or emergency contacts, to avoid confusion or interference.

The most likely explanation for why a penetration tester cannot scan a server that was previously scanned successfully is that the IP address is on the blocklist. Blocklists are used to prevent malicious actors from scanning servers, and if the IP address of the server is on the blocklist, the scanning process will be blocked.

Explanation
Quarterly is the minimum frequency to complete the scan of the system that is PCI DSS v3.2.1 compliant, according to Requirement 11.2.2 of the standard1. PCI DSS (Payment Card Industry Data Security Standard) is a set of security standards that applies to any organization that processes, stores, or transmits credit card information. Requirement 11.2.2 states that organizations must perform internal vulnerability scans at least quarterly and after any significant change in the network.
https://www.pcicomplianceguide.org/faq/#25
PCI DSS requires quarterly vulnerability/penetration tests, not weekly.

Explanation
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