How do I fix 500 Internal Server error when using "Open in Search" feature on some panels

[anmcgill]

I am encountering internal server errors when clicking on the open in search magnifying glass.  These are large queries (approximately 5.5K characters in the request).  

Some details:
 Splunk version is 8.2.2.1
 Single search head with 2 indexers
 Splunk is on-prem behind an Apache reverse proxy

I tried setting the LimitRequestLine and LimitRequestFieldSize to larger values in the Apache config with no success.

The Apache access_logs report the 500 error but no other really useful information.