R6400v2 Choppy Calls & Some Devices No Connection

My router is about 3 years old. Since COVID, I have been working at home and noticed I have choppy audio in/out on Teams calls on approximately 1 of every 10-20 calls. I have run speed tests while bad calls are happening and usually have 20-50mb connections. My router is upstairs and my laptop is downstairs. I have been running on the 2.4 band as it seems more reliable. I did a test one day and was 120mb hardwired, 75mb WiFi next to the router and 75mb WiFi downstairs (virtually identical). The choppy audio calls occur when we aren’t streaming or putting a heavy load on. I have tried turning off incoming and outgoing video when this happens with no change.

The second issue is occasionally our iphones won’t be able to use the internet for a couple of minutes while we are watching the fire stick. The firestick never skips a beat but we often have to turn WiFi off and back on on the phones.

I have the following devices: iPhone 4ea, iPad 1ea, laptop 3ea, tv 1ea, fire stick 1ea, WiFi receptacle 1ea, and printer 1ea. There are only 2 of us at home 90% of the time and when we experience problems. We have identitified the problems still happen when neither of us is steaming.

I’ve had multiple people from Comcast test our cable and router including resetting with no change. I’ve also unpowered/repowered all equipment abd devices abd disconnected and reconnected dozens of times.

The first issue is a big deal because it may jeopardize continuing to work at home. Are there settings I can change or should I change out for a mesh system?