Nas Model: DS216+II
DSM version: DSM 6.2.2-24922 Update 4
PSM version PlexMediaServer-1.19.1.2701-6327e27bf-x86_64(1).spk
BT Smart Hub.
I am new to Plex and have a free account. I have been considering buying a lifetime Pass for Plex but will not purchase one until I can get my free version working correctly

I have various shares on my DSM with content on them named in the correct format. I am able to see content on some of my created Libraries but on others I get
“There was an unexpected error loading this library”
I have tried reinstalling Plex also resetting modem, remaking the libraries, resetting my NAS and restarting my Mac but nothing seems to work 
I am now very frustrated and at a loss what to try. May I ask if any kind Forum member has the time to please advice on what to do next. So many questions I do not fully understand e.g.:
Should I use Port forwarding (I do not even know what that is)
In Plex/Settings/Remote Access/ I have a red circled exclamation mark showing?
And I cannot enable remote access.
My private Ip is 192.168.1.106:32400 with green arrow
My Public IP is 86.173.250.156 : 32400 with hared cross
Is this correct as I have think the 32400 is a port??
Will this be rectified if I buy a Pass.
Please can anyone advise on any suggestions I enjoy learning about Plex learn and will attempt any recommended advice.
Kind Regards
Gary