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.

Successful exploits could cause network disruptions, service outages, or data corruption, which could affect the connectivity and functionality of the oil rig network. Patch installations, application failures, and bandwidth limitations are less likely to be related to the penetration testing activities.

https://nmap.org/book/scan-methods-ack-scan.html

https://kalilinuxtutorials.com/foca-metadata-hidden-documents/
FOCA (Fingerprinting Organizations with Collected Archives) is a tool that is used to find hidden information in documents available on the web. It can be used to extract metadata from documents such as PDF, Microsoft Office, OpenOffice, and others. The metadata can include information such as the author, creation date, and software used to create the document. FOCA can also extract information from the document's properties such as the title, keywords, and comments. This tool can also identify specific keywords and patterns in the document and can be useful in identifying sensitive information that may have been inadvertently left in the document.