10.15.3 and 10.15.4 Catalina Persistent Wi-Fi Speed Drops - Tx Rate Drops

Hello,

I've recently started to notice severe speed drops with the Wifi on my Mac. I've narrowed down the problem to some kind of a software issue with OS X Catalina. I've updated from 10.15.3 to the supplemental 10.15.4 update today however it made no difference.

Problem:

• When performing a speed test the Tx Rate drops from 1300 / 867 Mbps down to <100Mbps almost immediately. On the speedtest the download speed consequently falls from 230Mbps to about 60Mbps or less.
• Outside of speed testing this causes issues with lag during video streaming, inconsistent download speeds etc.

My reasoning as to why this is a software problem with the OS X Catalina:

• I have Windows 10 installed in bootcamp on the same machine and when I ran a speed test on the exact same network there, it is consisntely 246Mbps from start to finish of the speed test and I experience no issues at all. This leads me to believe it is not a hardware issue with either the laptop or the network but a software issue with the Mac OS X.
• 802.11ac Wi-Fi works flawlessly at ~240Mbps accross all devices in my network. This includes my iPhone 11
• I haven't changed anything on my network recently and it was working perfectly fine at full speed on my Mac for at least 3 years with the same router and laptop.
• Issue is persistent and no amount of restarting of either the laptop or router has any effect.

Troubleshooting steps already tried with no effect:

1. Remove all of the relevant Wi-Fi preference files in SystemConfiguration folder and reboot
2. Create new network location and apply
3. Connect to 2.4Ghz network to check for stability - same problems except speed drops are even more severe and the connection becomes at times unusable.
4. Reset NVRAM - Done and no effect
5. Run system updates - Updated to 10.15.4, no outstanding updates in App Store - no effect
6. Checked network activity in activity monitor - nothing unusal using significant bandwidth
7. Tried different browser - same issue on Chrome and with Steam game downloads
8. Restarted router
9. Turned off Apple watch
10. Turned off Bluetooth
11. Rebooted in Safe Mode - Same issue

My MacBook:

• MacBook Pro (Retina, 15-inch, Mid 2015)
• Card Type: AirPort Extreme (0x14E4, 0x152)
• Firmware Version: Broadcom BCM43xx 1.0 (7.77.111.1 AirPortDriverBrcmNIC-1600.4)
•  Software Versions:
  •  CoreWLAN: 13.0 ((null))
  •  CoreWLANKit: 13.0 ((null))
  •  Menu Extra: 13.0 ((null))
  •  System Information: 12.0 (1500)
  •  IO80211 Family: 12.0 (1200.12.2b1)
  •  Diagnostics: 1.0 (910)
  •  AirPort Utility: Not Installed

Router:

• Virgin Media Hub 3.0

I've ran out of things to try at this stage. Anybody experiencing the same issues?

Thanks,

Kamil