Up until last week I could easily access my Plex server using the URL https://app.plex.tv/web/app from several Macs without problems.
A few days ago, I got the 'server unavailable' message, and have to select 'Reload app insecurely' to see my content every time I use Plex.
Setting 'Allow Fallback to Insecure Connections' to 'Always' or 'On same network as server' makes no difference.
Any ideas what is causing this?