Wifi, range 8m, ping 51638.594 ms, normal?

Question

WiFi

Hello, I'm having trouble with my wireless connection.
There are:
1. The Zyxel Kinetic Giga router is located on the first floor.
2. Devices that work with this router on the second floor.
3. Private house, no other Wi-Fi networks nearby.
Problem:
On the second floor, reception is, let's say, unstable.
For example, the direct distance to the router is about 8 meters, on the way to the router there are two internal walls of the house (15 cm) and a floor slab. The connection is sometimes quite stable, ping to the router is about 1.5-40 ms. Sometimes absolutely insane - ping to the router 5000 - 100000 ms (increases linearly, then also linearly decreases) and there is no connection. Wifi connection does not fall off, it is stable. There are no intermediate options, or everything is bad or everything works.
The laptop that communicates with the router shows 802.11n, RSSI: 75-77.
If the distance is reduced even by 1 meter, we get a stable connection, ping 1.5-40 ms, RSSI: 70-72 The
question is, what is it and how to deal with it?
UPD:
I turned off all possible signal sources, conducted a test with a microwave, two times the microwave killed the connection almost completely, and after it worked, the connection was not restored, the ping remained around 50,000 ms.
After that, he turned on the microwave a few more times, which did not affect the quality of the connection at all, the ping was within 15 ms.
At the same time, when the microwave is turned off and generally turning off everything that is possible, there are still communication problems.

Answer 1

Most likely - this is a router bug, change the frequency \ update the firmware \ change the mode from n to g and then check.
It is better to set the wifi speed lower (let's say 25MB in G mode).
Those. there is an error in determining the connection speed or distance to the client (most likely) and because of this, the router tries to adjust the link speed and everything breaks.

Answer 2

Remove any wireless mice nearby, move the microwave away from the wall)