Create Test Records and Provide Permission for Support to Replicate the Issue

Reliably reproducing an issue is the most important detail needed for any case investigation. Stating that unexpected behavior is occurring application-wide or for all records and users is too vague to begin troubleshooting. Narrow down the behavior to a specific click path, record, or application area and provide direct links to examples. Include a brief explanation of expected versus actual results.
To help expedite your case investigation, ensure that both affected users and an admin user Grant Salesforce Support Login Access to your organization. One month of access is recommended and users can expire it early once the case concludes.
Note: Each user must individually set and maintain login access. Support Engineers can only log in as one user at a time and cannot impersonate another end user via the Administrators Can Log in as Any User feature.

Replicating the Issue in a Sandbox Is Critical

If an issue is identified in production, Support may require you to test the same scenario in a sandbox environment. Systematic removal and re-introduction of customizations in a sandbox helps identify whether the issue is caused by core Salesforce functionality or by client-side customizations. Disabling or removal of customizations may not be possible in a production environment due to business impact.
If the issue does not occur in your currently available sandboxes, Create, Clone, or Refresh a Sandbox to obtain a recent copy from production for troubleshooting.

Ask Impacted Users to Document Detailed Information for Intermittent Issues

Collecting detailed information helps identify patterns or specific click paths that may lead to a consistently reproducible scenario. At a minimum, gather the following details from impacted users:

1. Affected User name
2. Exact date and time the issue occurred, including time zone
3. Exact error message or description of the problem (provide a screenshot if possible)
4. Links to affected records or application areas
5. Exact actions or click path the user took leading up to the unexpected issue — be as specific and thorough as possible

The more examples and detailed information users can provide, the better. Consider whether impacted users share the same profile, whether the issue occurs during a specific time window, or whether it is localized to a specific office location, user, browser, or local machine.

Issue Is Not Reproducible While Impersonating a User or Unable to Grant Login Access

If the issue does not reproduce while using granted login access, consider creating a test user with the affected user's profile and assigning the Support Engineer's Salesforce email to that user. Reset the password after changing the email to allow the Support Engineer to log in directly as an example user.
If your company policy does not allow affected users to grant Support login access, create a Developer sandbox (this sandbox type does not include production data). Input sample or dummy data to reproduce the issue and then grant access to Support for investigation.
If the issue is not reproducible when Admins or Support use granted login access as the affected user, this indicates a localized issue caused by something external to the Salesforce application. Engage your internal IT or Network teams to review the affected user's local machine, browser, geographic or office location, local network, and internet service provider.