Can't listen to two pairs of stereo paired speakers at the same time

Issue: I can not listen to two pairs of stereo paired speakers at the same time (one in the bedroom and one in the living room).

I purchased my first pair of One SL speakers on 12/01 and got a second pair a few days later on 12/11.

First let me say that the One SL as a stereo pair sounds amazing! That is also why this issue is so frustrating. According to the Sonos app on my Galaxy S9+ running Android 10, I have “Living room” and “Main Bedroom” as my speaker target options. Like I have mentioned, I have a pair of One SLs in each room. I have created stereo pairs with both. But this only works if I listen in one room or the other. If I try to select both rooms, I lose stereo pairing in one of the rooms. In some cases, despite what the animated equalizer icon indicates, I lose playback in one of the rooms entirely.

If I deselect one of the two rooms, three things tend to happen: 1) Playback resumes (if I lost it) in the remaining room selected 2) whatever track I was listening to starts over and 3) stereo pairing once again operates. 

Just listen to music in the bedroom? Stereo works. Just listen in the living room? Stereo works. Try to select both rooms (or pairs of speakers) and my issue occurs. What. The. Heck? I thought Sonos was a pioneer in multi-room, multi-speaker playback. That was sort of its whole shtick from the start. 

I did a factory reset on all for speakers. 

I used the default list to name my rooms or my speakers or my speaker’s rooms (Sonos needs to do a better job with this aspect of its system. How about a name for the speaker then place that speaker in a room in the house like you do with most smarthome items).

I removed and added and removed and added stereo pairing

I grouped and ungrouped

I am at my wits end here. I really do not want to return my 2nd set of speakers but I only purchased them for the stereo feature. If I want mono speakers, I’ll just keep using the many Google Home speakers I already own. 

In case this could be related to my home network here are the details:

My home Internet and wireless network are very stable and fast. ISP: Comcast with 250 Mbps download (consistent); Router: 1st generation Google Wifi with one additional access point. Main access point is in the living room (with one pair of speakers). Mesh/secondary access point is in the bedroom with my other set of Sonos speakers. I had no problems adding the SL’s to my phone app and my home network. 

Thank you in advance for your assistance.