Just to clarify, none of these factors seems to be affecting the device, correct?
It's quite hard to say what could be causing these issues, but I would be leaving toward the environment. Of course, hardware failure should also not be ruled out. One way this could be checked is if the spikes are long enough (>5min), the RUT240 could be rebooted, and after it boots up, check if the ping still has a big delay.
Have you tried a different wireless device to check if this is device specific or is always happening in the RUT240?
Also, make sure you are on the latest firmware.
Best regards,
DaumantasG