Will this issue happen on both 2.4G and 5G? How about the wired connection? You may plug a computer to the router with an Ethernet cable to have a check.
If only wireless has the disconnection issue, you can fix the channel to 1/6/11 and change the channel width to 20MHz.
If the wired PC has the same issue, you may need to contact your internet provider to check the line and the modem, or connect the PC to the modem directly to confirm the modem's performance.

Besides,is your router with the latest firmware? what's the hardware version of it?
Had wifi disconnecting issue on 5G before, got a beta firmware to solve the issue.