Chromecast relies on mDNS. "Multicast Optimization" parameter is meant to handle real multicast traffic (multicast switching feature). since mDNS send queries via IP multicast any "Multicast Optimization" will impact the mDNS as well, please see the image below which is an extract of the RFP 6762 (mDNS)
Apparently the Multicast optimization algorithm in the Wlan Service has something wrong because after I disabled it the Chromecast devices and google home devices starting to work well, before this change these devices were working really bad. Try it and let us know.
Hi, I am big fan of Chromecast and I have lot of them in my house, in my experience the Stellar performance with any multicast traffic was not good until the release 188.8.131.52 or 19 where I have noticed a great improvement and now I'm able to cast videos to any Chromecast almost without issues but before these releases the Chromecast devices were not visible for my video apps like youtube, netflix or any other. So try the 184.108.40.206 and let me know.