Hello,
To answer briefly, yes, the problem could be due to temperature.
The router is rated to work within temperature ranges between -40 - 75 °C. However, operating the device as the temperature approaches it's limit for an extended period of time will certainly result in reduced performance. If the device operates in high temperature environment, it creates a kind of loop, where device temperature increases, which leads to increased power consumption by the device, which again increases the device temperature and heat in your electrical panel.
Best regards,