Content Delevery API filter by createDate blues

Hi,

I have a strange issue where a filter using createDate or updateDate does noth return anything from Content Delivery API.. whatever filter i else use, works fine.. The setup is Umbraco 13 using Azure Search with ExamineX (dou to load balancing). each time i filter by either cerateDate or updatedate, there is an error entry in the log, but it doesn’t really put me in the right direction:

Azure.RequestFailedException: Invalid expression: Expression expected at position 387 in '(search.ismatchscoring('x__IndexType:content', '', 'full', 'any') and search.ismatchscoring('x__IndexType:content', '', 'full', 'any') and (search.ismatchscoring('culture:da\-dk', '', 'full', 'any') or search.ismatchscoring('culture:none', '', 'full', 'any')) and search.ismatchscoring('published:y', '', 'full', 'any') and ((createDate gt 2023-01-01T23:00:00.0000000Z and createDate lt )))'.
Parameter name: $filter
Status: 400 (Bad Request)

Content:
{"error":{"code":"","message":"Invalid expression: Expression expected at position 387 in '(search.ismatchscoring('x__IndexType:content', '', 'full', 'any') and search.ismatchscoring('x__IndexType:content', '', 'full', 'any') and (search.ismatchscoring('culture:da\\-dk', '', 'full', 'any') or search.ismatchscoring('culture:none', '', 'full', 'any')) and search.ismatchscoring('published:y', '', 'full', 'any') and ((createDate gt 2023-01-01T23:00:00.0000000Z and createDate lt )))'.\r\nParameter name: $filter"}}

Headers:
Cache-Control: no-cache,no-store
Pragma: no-cache
client-request-id: 6f110674-190e-4c57-b723-5fb8400fd9db
x-ms-client-request-id: 6f110674-190e-4c57-b723-5fb8400fd9db
request-id: 6f110674-190e-4c57-b723-5fb8400fd9db
elapsed-time: 31
Strict-Transport-Security: REDACTED
Date: Tue, 12 Aug 2025 14:59:38 GMT
Content-Length: 514
Content-Type: application/json; charset=utf-8
Content-Language: REDACTED
Expires: -1

   at Azure.Search.Documents.SearchClient.SearchInternal[T](SearchOptions options, String operationName, Boolean async, CancellationToken cancellationToken)
   at Azure.Search.Documents.SearchClient.SearchInternal[T](String searchText, SearchOptions options, Boolean async, CancellationToken cancellationToken)
   at Azure.Core.Pipeline.TaskExtensions.EnsureCompleted[T](Task`1 task)
   at Azure.Search.Documents.SearchClient.Search[T](String searchText, SearchOptions options, CancellationToken cancellationToken)
   at ExamineX.AzureSearch.AzureSearchResults.b.A()
   at ExamineX.AzureSearch.AzureSearchResults.A[A](String, Func`1, Func`1)

Both Azure and ExamineX packages are the latest versions (for umbraco 13).

Any thoughts?

/ulrich