A sharp jump in ping in games on Wi-Fi 5GHz. How to decide?

Question

Computer networks

Router ASUS RT-AC57U(AC1200), firmware from Padavan/Linaro(if it helps), phone Xiaomi Redmi 5 Plus, Samsung Galaxy S8 Plus. The 5GHz network is one for the whole house, 2 devices are active while playing the same game, a sharp jump in ping can occur at different times. Actually how to fix it?
The firmware has changed, the settings are set to maximum performance, the air is empty, the coverage of the apartment is 100% (the signal is not lower than 80dBm, on average 60-70), the Internet is 600mb/s, there is no load at all.

Answer 1

Wi
- Fi 5GHz

Answer 2

If the ping is in your wifi network, then you can check the channels (1-13) and select the least loaded one.
If the provider part, then ask questions to the provider.

Answer 3

About the fact that the air is empty - the author is mistaken. He doesn't live on the moon. Wifi is a radio that is constantly affected by the environment. Therefore - only a cable. And log delays and talk with the provider about the quality of the channel.