I too have been encountering issues for the last few days, since the Plex for Chromecast app has been rewritten and now sports a new interface.
All 1080p or lower media in my libraries, as far as I can tell, still stream as in they always have in the past prior to the update, however, I am now noticing lag in some of my 2160p media (HEVC-H265-HDR), not all. For the ones that do suffer the lag issue, some are getting it worse than others, to the point where they will stop playing after 5 or 10 minutes, just hanging. Note that all of them used to work without any buffering/lagging/hanging issues until earlier this week, and this I am 100% sure of.
- The instances I am reporting are all being streamed on my local network, and not remotely.
- Vizio 2017 P series built-in Chromecast.
- PC wired to network, TV on wireless 5G.
- No changes have been made on my home network before the issue started.
- All media, 2160p included used to stream without a hitch, until earlier this week.
Another weird behavior I have been experiencing, which started exactly the same day, when the Plex for Chromecast app update occurred, is that I can no longer connect to my media server securely using Plex Web Apps, from within my own local network. I know this does not sound related to Chromecast, but it did start happening at the same time. If I tried to access Plex by opening it from the Plex Media Server tray icon (127.0.0.1:32400), no issues. However, when trying from 192.168.xx.xx:32400, or from the Android app, or from TV apps (2 different TVs), or from https://plex.tv, I will either get an insecure Indirect connection to my own server, or none at all (Unavailable), on my own LAN! Even weirder is that from outside my own LAN, everyone gets fully connected to my server, directly and securely.
After doing a bit of Google searching, I found that with my network setup (I am behind a pfSense router), I should add in the DNS Resolver section an exception for the plex.direct domain so it uses an alternate DNS server. Once I made that change, I am now able to connect directly and securely to my PMS. What’s weird is this solution was written in a forum and dates back to 2015. I have been behind pfSense for at least one and a half year, and never needed such a tweak before, this only started the same day the Chromecast update came. Doesn’t make much sense I know, but this is my experience, as far as I can explain it.
Hopefully this may help enlighten developers with the lag issue we are experiencing.