A problem investigation had been previously closed, because the risk was accepted, in favor of using the workaround, instead of applying the fix. After a couple of weeks, the issue starts to occur…

There is no 7-day hard lock that permanently prevents a Problem from being re-opened; the Re-Analyze action is available to Problem Managers regardless of how long ago the Problem was closed.

ServiceNow Problem Management provides a 'Re-Analyze' action specifically for Problem Managers to reopen a previously closed problem investigation and return it to an active root cause analysis state. This action is role-appropriate and designed for scenarios where a known error or accepted risk needs further investigation due to recurrence or increased impact.

The Problem Assignee does not have a 'Re-Open' button in standard Problem Management; re-opening a closed problem is a managerial action performed by the Problem Manager.

An Administrator clicking Re-Open is not the documented process; the Re-Analyze function is specifically granted to and intended for the Problem Manager role, not a generic administrator action.