Low Wi-Fi speed on AXT-1800 after latest firmware update to v. 4.2.0

Hi there!
I faced with low wi-fi speed on my AXT-1800 after latest firmware update to v. 4.2.0
On v. 4.1.0 it operated fine, with high speed of about 500 Mbps, after update I had a low speed of about 140-150 Mbps but if I enable WireGuard client I got 200 Mbps that matches my server bandwidth.
After a rollback to v 4.1.0, the speed returns to normal.
What could be the reason?

Thanks for the feedback, I will actually get the router to test on Monday.