Please tell me which version of the firmware is currently installed on router?
Also, if possible, could you send the troubleshoot file to PM?
It can be downloaded at:
WebUI -> Administration -> Troubleshoot
With it, I will be able to examine in detail for what reason this is happening.
When you enter the WebUI, you see information about how much router RAM/FLASH memory is free. Tell me this information, please.
Waiting for your reply!