SharePoint cannot access Workflow details anymore

Question

I did the following:

$oldWorkflow="MyOldWorkflow";
$oldAssoc=$list.WorkflowAssociations.GetAssociationByName($oldWorkflow,"en-US");
$list.RemoveWorkflowAssociation($oldAssoc);

After that I can see that the workflow does not exist anymore. But on each Item that had the workflow before I receive an error when trying to display the workflows:

Getting Error Message for Exception System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.ArgumentException: Column 'Reservat' doesn't exist

I never had a column with that name. After adding that column manually to the list, the error messages changed to:

Application error when access /_layouts/15/Workflow.aspx, Error=Object reference not set to an instance of an object.

Any chance to solve this mess? (The old workflow does NOT exist anymore as WSP)

UPDATE: I can still find the workflows using Powershell:

     foreach ($wf in $item.Workflows) 
  if ($wf.ParentAssociation.Name -eq $oldWorkflow) 
                ...

But in the same time $list.WorkflowAssociations.GetAssociationByName does NOT return the workflow

Answer 1

I solved this. Note for all those who came here by google: This is not a good practice for removing workflows, but only a solution if you already messed up your workflows in SharePoint. (like me)

$oldWorkflow="MyOldWorkflow";
    foreach ($item in $list.Items) {
            foreach ($wf in $item.Workflows) {
                if ($wf.ParentAssociation.Name -eq $oldWorkflow)  {
                    Write-Host ("[{0}] Workflow '{1}' will be removed" -f $item.Title, $wf.ParentAssociation.Name);

                    $itemsToRemove.Add($wf);
            }
        }
    }
    ForEach($item in $itemsToRemove) {
        $man.RemoveWorkflowFromListItem($item);  
    }

Answer 2

This is the cure for most any SPDesigner misbehavior. It also worked for me in a situation very similar to the issue in this post.

1. Close SPD2013
2. Delete everything at %USERPROFILE%\AppData\Local\Microsoft\WebsiteCache
3. Delete everything at %APPDATA%\Microsoft\Web Server Extensions\Cache
4. Go to SPD2013 options –> General –> Application Options –> Uncheck the “Cache site data across SharePoint Designer sessions”