Different phones, though the biggest culprate and worst wifi reception is an iPhone X (two of then, both are horrible for WiFi). Had to add an access point to the house for them because they didn't work on 5G where other Android and older iPhones did just fine.
2.4GHz is really crowded where I live, hence the desire to stay on 5GHz. Secondary reason, max bandwidth is lower on 2.4G (about 30Mbps).
Yes but do you notice a problem if the phone is on 2.4 ghz?