404 After Service Restart

(from github.com/j-barnes)
After trying to restart our FESS / Elasticsearch service we are currently receiving a 404 error. The solution has been working fine for 6 months with no changes.

We tried clearing configsync using:
service fess stop; curl -XDELETE http://localhost:9200/.configsync; service elasticsearch restart; service fess start

Fess: 12.3.0
Elasticsearch: 6.3.2


(from github.com/marevol)
Fess 12.3 does not support Elasticsearch 6.3.
See Download page.

(from github.com/j-barnes)
Issue resolved. The problem was caused when trying to use a OR query in the Key Match. Removed and everything is working as intended now. Thank you!