This has been worked on in multiple threads, so I guess it’s unreasonable to expect updates from the Plex team in every thread (I’ve said it before and I’ll say it again: public visibility of bug tracking/tickets would be super helpful).
IMHO, the most productive work on the problem (along with this thread) has been here:
tl;dr Plex started using a new (to them) open source library to parse the XML response from UPnP devices on the LAN and I believe the implementation is responding badly to data provided by routers running the miniupnpd software and going into a CPU loop.
Best current workarounds are to either disable UPnP (no need to disable NAT-PMP, just UPnP) on your router or keep your PMS instance on 1.14.0.5470
