Confluence question topic and unanswered filter inconsistency between datacenter nodes

Issue description

Within Confluence datacenter version 5.10.8 and Confluence question plugin version 2.4.19, we've found 2 problems:

1. the topic created on node 1 does not appear on node 2
2. the answered question being done on node 1 is still showing in the unanswered filter on node 2

Reproduction steps

1. Topic issue:
   • Set up a Confluence datacenter with 2 nodes
   • Create a new topic on node 1
   • Check the topic list on node 2
2. Unanswered question filter issue:
   • Create a new question on node 1 then add an answer
   • Check the unanswered filter on node 2

Expected behavior

1. Topic: the new topic should show on node 2
2. Unanswered filter: the answered question should not show in the filter result on node 2

Actual behavior

1. Topic issue: the new topic does not appear on node 2
2. Unanswered filter issue: The answered question appears in the unanswered filter result on node 2 and showing that there is an answer.

Workaround solution (if you can not upgrade to Confluence 6 shortly)

Disable and enable the Confluence question force the cache repopulation, however, the same issue will occur again on the newly created topic or question until next restart.