Whelp, figured out why this bug has yet to be diagnosed (and may never be fixed). Looks like webOS is the least used Plex client out there, so it’s probably not worth the time to fix for them.
Shame since their TVs are constantly among the top options available
EDIT: While downgrading to 1.16 may seem like an understandable workaround, it’s not. The latest releases have import security patches that fix exploits in the older versions of PMS. Even if webOS is not a widely used platform, the bug is bad enough that it is causing people to use vulnerable versions of the software, indicating that Plex really should be looking to patch this with a bit more urgency.
