Google Messages: "This RCS chat is no longer end to end encrypted." Why is RCS so flaky?

I have recently ditched Signal and started using Google Messages with RCS instead. Many times, sending fails, either from my side or from the other party (several different people, all using Android). I see these RCS warnings even though none of us are changing any settings about RCS, other stuff in Google Messages, or even anything else on the phones; it also seems unrelated to whether the phones are on 4G, WiFi, or roaming. RCS just feels like a dice-roll. - "This RCS chat is no longer end to end encrypted" - *messages fail* - *time passes* - "This RCS chat is now end to end encrypted" - *messages work fine* - ***repeat*** What can we do to make RCS work reliably?