This is because Linksys has a bug in the way they monitor and calculate their MTU. The RV016 has a feature that allows you to assign up to
7 ports as WAN ports. This feature does not have an option to only have 1 WAN port (the minimum is 2) bcause of this, each packet is
analysed when it hits the RV016 and the MTU monitoring function checks to see average MTU size and it’s historical effect on latency.
I assume you had the same issue we did. When you reset the router to factory settings did the first few SSH connections stay connected longer
than the ones the followed? Ours did! This tells me that it is possible that the higher the percieved load, the worse the problem gets.

By setting the MTU manually you caused the router to stop messing with the MTU. That is why SSH now works. Linksys will never admit
to it but I am convinced they have an error in their Automatic MTU setting.

Thanks for posting this, I am glad to know I am not the only one that had this issue.