I continued to investigate as there was no help from plex staff and I found that the problem is due to new iocage jail infra. The problem I had is very similar to No metadata download - FreeNas 11.2 Iocage Jail and I solved the problem with above link suggestions with addition to vnet settings as specified here https://forums.freenas.org/index.php?threads/plex-jail-metadata-video-playing-problem-in-11-2-beta3.69960/
Incase anyone migrates to iocage jail and run plex you are likely to run into this problem.
