I have not seen RAM usage reach 100% - or at least thought to look at the usage whenever I was troubleshooting issues, or monitoring the system. Based on what I've read, the RAM consumption, is an indicator of load on the system. If you look at the Traffic Analyzer "Statistic" section, you can see which clients or App is consuming resources/bandwidth. Looking for HIGH usage and that would give you an indicator at least of the client/app that may be the issue. If you have no "HIGH" usage, and the RAM is spiked at 100%, then there may be something else going on with your router. Recommend power cycle the device - I regularly "scheduled" reboot the router, I have found that this keeps the system running smoothly and I have little issue with the device.
Be @ Peace -
I guess we have unique situations. I've been looking for other answers to this but haven't come across anything online. I even staring looking to see if I could upgrad the RAM, but that seems like a non-starter.