webportal error event, no workitems visible in cireson portal v5.05

On our testenvironment we're experiencing some strang behaviour. We're not seeing any workitems on the portal in active work (eg. my admin account and my domain account, admin account in no queue, domain account in IT queue and corresponding user role).
A test user, within a different queue and user role, did see the proper workitems, but when i added a new queue (releaserecords) to the userrole this user is a member of, also this account does not show any workitems at all (except for team work) .
When i take a look at the evenlog i get these errors every minute (which corresponds with the workitem update interval of the cireson cachebuilder)

System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.
   at System.Data.SqlClient.SqlBuffer.get_DateTime()
   at System.Data.SqlClient.SqlDataReader.GetDateTime(Int32 i)
   at Cireson.ServiceManager.DAL.Wrappers.SqlDataReaderWrapper.GetDateTime(Int32 i)
   at Cireson.ServiceManager.Services.Implementations.WorkItemGridService.GridWorkItem(ISqlDataReaderWrapper reader)
   at Cireson.ServiceManager.DAL.Database.<ReadFromStoredProcedure>d__5f`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Cireson.ServiceManager.Services.Implementations.WorkItemGridService.<>c__DisplayClass27.<GetGridWorkItemsAllAsync>b__26()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Cireson.ServiceManager.Services.Implementations.WorkItemGridService.<GetGridWorkItemsAllAsync>d__29.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at CiresonWebConsole.Controllers.api.V3.WorkItemController.<GetGridWorkItemsAll>d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at CiresonWebConsole.Controllers.GridController.<Data>d__20.MoveNext()

SCSM is having no issues at all. Eg. the admin account is showing the proper data.

Any help is welcome.

Kind regards,

Paul