Others have addressed the technical side, but legally, the router is almost certainly certified under part 15 of the FCC rules, and it probably carries a sticker on the bottom that says:
"This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation."
That means that, legally, part 15 devices are very low on the totem pole. If there are problems, the legal solution is to stop using the part 15 device unless and until the owner of the Part 15 device resolves the problem technically, perhaps by going back to the manufacturer. If it causes harmful interference, the owner of the device must shut it down and not operate it until the cause of the interference is corrected. If it receives interference that causes it to malfunction, the owner has to deal with it or shut it down -- the owner can't demand that the other device be shut down, or somehow reduce or eliminate the emissions that are causing the interference.
When you are the owner of both the interfering device and the device receiving interference, this legality is pretty much moot. You can decide which device to shut down until the problem can be dealt with technically. It becomes more relevant when a Part 15 device has a conflict with a neighbor's device operating under a different part of the regulations, such as a ham radio station, or a business band radio, or a broadcaster, etc.