I’m having the same issues with intermittent missing messages from groups of 3+ with 1+ android members.
Below are the variables/configuration in which I encounter the messaging problems… it basically happens in all configs…
Phone Model: iPhone 12 Pro 512GB (MGJW3LL/A)
iOS Versions: 14.1 & 14.2
Carrier: AT&T
Carrier Plans: 5G Unlimited Elite & LTE Unlimited Plus Enhanced
Typical Cellular Bars (home): 2 - 4 (away)
Wifi Calling Configs: Enabled & Disabled
Cellular Data Configs: 5G Auto & LTE only
Wifi Configs: Enabled & Disabled
Tried all recommended settings/fixes with no luck.
I heard iOS 14.3 Beta is out with a major “modem firmware” update. Fingers crossed…