When a PROFINET Device or a Module is marked red (error), does that affect other devices or modules?

No. They are not affected during a data exchange.

Is a diagnosis in the field device is deleted when I reset or restart the application?

This varies: Hardware problems are not solved by this, but errors by an incorrect parameterization are.

Can a controller delete or confirm the diagnosis of the PROFINET Device?

No, the PROFINET Device manages the diagnosis entries and sets the status of the modules. The PROFINET Controller merely confirms the receipt of incoming alarms at the log level.