CMS UI page editing validation starts failing unexpectedly

Hi

Validation of pages in UI will sometimes start failing, not matter which , usually after some uptime. Commonly detected when modifiing settings on the pages we use for global settings.

Sometimes it goes away when restarting the webbserver instance, sometimes not.

The script gets a 500 error.

This is what happens in the log:

2024-03-01 10:11:05.2502|ERROR|Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware|An unhandled exception has occurred while executing the request.|System.ArgumentNullException: Value cannot be null. (Parameter 'value')
   at System.ComponentModel.DataAnnotations.ValidationContext.set_DisplayName(String value)
   at EPiServer.Validation.DataAnnotationsValidator`1.ValidateInstance(Object instance, List`1 validationResult, ValidationContext validationContext)
   at EPiServer.Validation.DataAnnotationsValidator`1.ValidateInstance(Object instance, List`1 validationResult, ValidationContext validationContext)
   at EPiServer.Validation.DataAnnotationsValidator`1.Validate(T instance)
   ........

Cannot replicate the issue in development, so it's a pain trying the find the real cause.
It looks like Episerver suddenly looses its ability to get the displayname from properties.

None of the properties on eg the settings page have any name specified, could it be a localization issue?