Business Central onPrem service instances are starting with the default configuration

Dear @WAGNER Martin,

Thank you for providing the detailed description of the issue and for sharing your observations across multiple Business Central On‑Prem environments.

Based on the information available, the behavior you are experiencing where a Business Central On‑Prem service instance intermittently starts using the default configuration instead of its assigned instance configuration, resulting in WebSocket connectivity errors points to an internal instance initialization or service binding issue within Business Central itself.

For this type of tailored assistance, the Dynamics Support team is better positioned to provide recommendations based on your situation. In this case, the best way to further troubleshoot it is to report it to the related team. Please open the Contact Microsoft Dynamics 365 page and pick the support option that works best for you. This is a specific channel related to Dynamics. In there, you'll get the most qualified group of respondents, and other partners who read the forums regularly can share their knowledge or learn from your interaction. 

Please understand that as forum moderator, my primary goal is to provide helpful guidance and support through general troubleshooting steps. While I don’t have access to internal systems required to resolve account issues, I truly appreciate your understanding of these limitations. I genuinely hope the information I share helps guide you in the right direction, and I'm always here to assist as much as I can within my scope.  

I hope this information is helpful. If you need any further assistance, please feel free to reach out. I am here to help. Thank you very much for your understanding and cooperation.

The described behavior (Business Central on‑prem server instances occasionally starting with an unexpected/default configuration and then failing WebSocket connections on the client/API ports) isn’t documented in the provided material as a known issue for version 27, and there is no supported detection pattern or fix in the context beyond the general guidance on how to configure and start Business Central Server instances.

From the available information, only these directly relevant points can be stated:

1. Configuration changes to Business Central Server instances must be done through supported tools:
   • For older versions, the Business Central Server Administration tool or direct editing of CustomSettings.config was possible, but direct editing is discouraged because a typo or invalid value can prevent the service from starting correctly.
   • Starting with Business Central 2022 release wave 2 (v21), the Business Central Server Administration tool is removed and configuration should be done with the Business Central Administration Shell using Set-NAVServerConfiguration. This approach also handles required HTTP namespace reservations automatically when changing ports.
2. Changing ports or configuration directly in CustomSettings.config can cause startup and connectivity issues:
   • There is a known issue where changing port numbers directly in CustomSettings.config (for example, ClientServicesPort) can cause the Business Central Server instance to fail to start with HttpSysException (0x80004005): Access is denied until the correct HTTP URL ACLs are granted.
   • The recommended workaround is to use Set-NAVServerConfiguration instead of editing the file directly, or explicitly add the required URL ACL with netsh http add urlacl for the affected port and service account.
3. General guidance for configuration and restart behavior:
   • Configuration should be changed via Set-NAVServerConfiguration in the Business Central Administration Shell, which can apply some settings dynamically without restart; others require a service restart.
   • Direct edits to CustomSettings.config are not recommended because they can leave the instance in a non‑starting or misconfigured state.

The context does not provide:

• Any documented bug in v27 where instances randomly start with a default configuration.
• Any supported method to programmatically detect “default configuration” startups or to correlate them with instance names, dash characters, or WebSocket port assignment issues.
• Any monitoring or health‑check pattern specific to this scenario beyond standard service start/stop and connectivity checks.

Within the provided material, the only concrete, supported actions are therefore:

• Ensure all configuration changes (including ports) are made via Set-NAVServerConfiguration in the Business Central Administration Shell, not by directly editing CustomSettings.config.
• When ports are changed, rely on Set-NAVServerConfiguration to manage HTTP namespace reservations, or explicitly add them with netsh http add urlacl if needed.

References:

• Some known issues in Business Central on-premises
• Configuring Business Central Server in outdated versions
• Configuring and troubleshooting SQL Server Connections