It also blocks some streaming connections randomly.

I'm guessing it's because the ridiculous paid security program included in it isn't working properly. Even without a free or paid subscription, it somehow affects connections.

  @Sunshine Hi,

Hi, is your Archer AX80 working on Router mode or AP mode? 

It is positioned as the main device in router mode, I am not actively using the ISP device.

If your ISP device is a modem and also a router,  you could try configuring the Archer AX80 to AP mode(Case 1) to see if it solves the problem:

How to configure the TP-Link wireless router as Access Point

I'll try it at the appropriate time.

By the way, does the issue happen on all the client devices or only some specific devices? via WiFi only or wired connection has the same issue?

On all devices and Wi-Fi connection. 
I did not observe such a fluctuation in the wired connection.

Ps: I can say that the problem appeared with the last updated software version. 

Thank you for your concern.

  @Sunshine 

I never prefer smart connection on the network devices, because it is not very smart. :)

The connection type communicates with the devices as 2 separate channels and only smart home devices are connected at 2.4ghz band. There is 3 metres and one weak wall between me and the device. Despite this, the device is experiencing very serious performance loss or instability in some way. When I check the channels I use from the connection performance menu via the tether application, it states as excellent.