Answers.Body: <p>Answering my own question.
  On checking logs it was in fact missing civivolunteer custom fields.
  restored them from backup and all good now.</p>
  
  <p>Is this bad behaviour for an extension?</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-04-06T15:34:14.983Z
Answers.Text: How did you delete the data?  Your reference to deleting 'mysql data' suggests you might have done this with direct sql - in which case the extension doesn't get chance to clean up any dependencies resulting in an inconsistent state.  On the other hand if you deleted via GUI and/or API then it should cope but if not, log an issue.
Answers.UserDisplayName: Aidan
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-04-06T11:26:21.467Z
Answers.LastActivityDate: 2020-04-06T11:26:21.467Z
Answers.UserDisplayName: LesleyJill
Body: <p>civi 5.9.13 WP 5.2.2
  civi In a contract screen activities tab no activities are listed
  error popup says "DataTables warning: table id=DataTables_Table_0 - Invalid JSON response. For more information about this error, please see <a href="http://datatables.net/tn/1" rel="nofollow noreferrer">http://datatables.net/tn/1</a>"
  EEK!
  I've recently deleted various mysql data related to civivolunteer - hope this didnt break anything</p>
  
  <p>PS I tried the fix here: <a href="https://civicrm.stackexchange.com/questions/21796/datatables-warning-cannot-view-activities-after-upgrade-to-4-7-28">DataTables Warning: Cannot view Activities after upgrade to 4.7.28</a>
  didn't work</p>
  
Tags: <activities><json>
Title: Activities not displaying and weird json message
ThreadText: # Activities not displaying and weird json message
  
  (Asked by: username_0 on 2020-04-06)
  
  civi 5.9.13 WP 5.2.2
  civi In a contract screen activities tab no activities are listed
  error popup says "DataTables warning: table id=DataTables\_Table\_0 - Invalid JSON response. For more information about this error, please see <http://datatables.net/tn/1>"
  EEK!
  I've recently deleted various mysql data related to civivolunteer - hope this didnt break anything
  
  PS I tried the fix here: [DataTables Warning: Cannot view Activities after upgrade to 4.7.28](https://civicrm.stackexchange.com/questions/21796/datatables-warning-cannot-view-activities-after-upgrade-to-4-7-28)
  didn't work
  
  **Tags:** activities, json
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_0 on 2020-04-06. Score: 1
  
  Answering my own question.
  On checking logs it was in fact missing civivolunteer custom fields.
  restored them from backup and all good now.
  
  Is this bad behaviour for an extension?
  
  > **Comments:**
  > **username_1**: How did you delete the data?  Your reference to deleting 'mysql data' suggests you might have done this with direct sql - in which case the extension doesn't get chance to clean up any dependencies resulting in an inconsistent state.  On the other hand if you deleted via GUI and/or API then it should cope but if not, log an issue.  
  
  ---
  
  