I may be wrong, but my hunch is that the router is not being fully reset.
Download the correct firmware for the router model that you want to use (I recommend RMerlin 384.16 Beta 2) and make sure to verify it with something similar to
this.
I would do the following in this strict order and if the issues continue, return for refund/exchange.
- Power off the router by pulling the power plug from the router and the AC wall plug too.
- Power off the modem/ONT.
- Remove all USB devices attached to the router. Do not re-insert them for this test.
- Plug in the router's AC power plug to the wall outlet.
- Make sure the routers power switch is in the off position.
- Plug in the power plug to the router.
- Hold down the WPS button and keep holding it until the router reboots/turns off while you turn the router on using the power button.
- When the router boots up, it should be in the Setup Wizard. If it isn't, repeat the steps above until it is.
- Use the following URL to bypass the setup wizard and go straight to the factory reset part of the GUI.
- http://router.asus.com/Advanced_SettingBackup_Content.asp
- Check the 'Initialize all the settings...' box.
- Click on the 'Restore' button beside it.
- After the router reboots, use the same URL above to flash the firmware you have downloaded and verified at the beginning of this post.
- After the router reboots, use the same URL to repeat steps 11, 12 and 13 above.
- Plug in the modem/ONT and connect the Ethernet cable to the router's WAN port.
- After the router reboots use the Setup Wizard to connect to your ISP and secure your router.
- Use a new (never before used) SSID that is 8 alphanumeric characters with no spaces, punctuation, smiley faces or other special characters.
- Use all-new (never before used) passwords that are 16 alphanumeric characters with no spaces, punctuation, smiley faces or other special characters.
- Use a new (never before used) username that is 8 alphanumeric characters with no spaces, punctuation, smiley faces or other special characters.
- Do not change any other settings or enable any other features.
- Do not insert any USB devices.
- After the router has been running for 15 minutes or more, reboot it once more.
Does the issue persist now? Does it persist after an additional reboot after it has been running for at least an hour?
If the answers to the last questions are yes, return/exchange it.
If the issues have been solved, I would format the USB drive you used in the router on a PC before you put it back into the router port.
Proceed to customize your router slowly and only changing one thing at a time. Testing as you go.
Do not use any saved settings (for the router or for any of the scripts you were using previously either).
HTH.