Wi-Fi disconnecting when "under load" At some point towards the end of last year (2019), Wi-Fi started frequently dropping off and then automatically reconnecting on my MacBook Air 2018.

At least two things happened around that time, that could have triggered the issue, but I do not remember when they happened and in which order, and whether it even was before or after the issue started occurring:  


macOS update from Mojave to Catalina,
light drop of the laptop, which didn't seem to have affected anything else.


Things I gradually noticed during the investigation:


My connection is 50Mbs down / 4Mbs up, and it seems to be easier to reproduce when uploading data rather than downloading. Consistently able to reproduce when on a Skype call.
Eventually able to reproduce when downloading a file from test FTP server, even with very low speed limit set on client side.
Able to reproduce at home with 802.11n (2.4 GHz) network.
Unable to reproduce at home with wired connection.
Unable to reproduce at home with any other device using wireless connection, including another mac laptop (MacBook Pro 2018), Android phone (Motorola moto G6), and Windows laptop (Asus Y50-70).
Unable to reproduce in the office, where network is mixed 802.11ac (5 GHz) / 802.11n (2.4 GHz).
When watching /var/log/wifi.log around the disconnect events, the following line caught my attention for some reason:

&lt;kernel&gt; AppleBCMWLANCore::getSSIDData(): Get failure: APPLE80211_IOC_SSID: -528342013



Various tweaks I tried, none of which helped:


Changing home router settings (transmission mode between b, g, n and mixed b/g/n; transmission rate; channel; channel width between 20 and 20/40 MHz; multicast rate)
Disabling IPv6
Resetting NVRAM
Wipe all WiFi settings from MacBook
Lowering MTU
I was eventually able to resolve it by following the suggestions from Bluetooth headphones disconnect a few seconds after connecting on macOS, namely:  


https://apple.stackexchange.com/a/344552 by Gummibando:


  Try resetting the Bluetooth module.
  Shift-Option click the BT menu bar item > Debug > Reset the Bluetooth 
    module.

https://apple.stackexchange.com/a/380827 by Kundan Burnwal:


  
  Delete /Library/Preferences/com.apple.Bluetooth.plist
  Clear PRAM according to Apple's instructions by rebooting and holding down Command +Option+P+R for roughly 20 seconds until either the second startup sound plays or Apple logo appears and disappears for a second time.
  



P.S. I think it is worth noting that the steps for resetting NVRAM and PRAM are the same, and did already try "the former", but that time it coincided with a minor macOS version update, which could have affected the reset procedure in some way.

Upd: unfortunately, pairing back and connecting a Bluetooth device (e.g., headphones) brings the issue back, so this whole workaround is just that — a workaround.