Creating api endpoints

For some reason we get this as warnings on our PSU instance:

Invalid configuration: endpoints.ps1
Object reference not set to an instance of an object

Several different endpoints but we get that for every endpoint created. Trying to call the endpoints results in:

Invoke-RestMethod : The remote server returned an error: (500) Internal Server Error.

We also cannot access pages with web forms (although we can create them). WHen trying to view such a page we receive:

This page isn’t working right now
can’t currently handle this request.

Running 4.2.19, have tried removing PSU, inclduing every directory in programdata and reinstalling. Same issue.

Have installed 4.2.20, issues remain.

You will need to check in the system log for a good error message. Search for [ERR]. It sounds like the API service may not be starting properly.

2024-05-03 08:59:14.868 +02:00 [ERR] Failed to read configuration file. endpoints.ps1
System.Exception: API environment is not running! Please ensure your environment is configured correctly.
at Universal.Server.Services.ApiGrpc.RemoveEndpointAsync(Endpoint endpoint) in C:\actions-runner_work\universal\universal\src\Universal.Server\Services\API\ApiGrpc.cs:line 195
at Universal.Server.Services.ApiService.RemoveEndpointAsync(Endpoint endpoint) in C:\actions-runner_work\universal\universal\src\Universal.Server\Services\API\ApiService.cs:line 247
at UniversalAutomation.Services.EndpointsConfigurationScript.OnReadAfterUpdateAsync(Endpoint endpoint) in C:\actions-runner_work\universal\universal\src\Universal.Server\Services\Configuration\Endpoints.cs:line 84
at UniversalAutomation.Services.ConfigurationScript`1.ReadAsync(String rootPath, Boolean initialSync) in C:\actions-runner_work\universal\universal\src\PowerShellUniversal\ConfigurationScript.cs:line 331

But we don’t have a directory named C:\actions-runner, so I have no idea what’s going on there.
Also, the PSU server is fairly locked down. No internet connection whatsoever. So all jobs checking for updates / license etc. will definitely fail, but I fail to see any obvious correlation to the issue at hand.
Server is 2022 21H2, latest (2024-04) patches, running the RDS role, has a valid certificate etc.