Although the wan link was flashing the entire evening as well as the wireless link on the modem, there were no drop off's for the last two days, since I connected to lan 2.
Fingers crossed that this was the actual issue. Some sort of break in a cable connection which even when tested (the lights showed on both connections as working) appeared as intact. So now it's a wait and see. And perhaps a modem replacement if this reoccurs.
Would be ironic if it were something like a slightly cracked Ethernet connector. The plastic part that you press down to lock it into place. Where if it gets damaged or simply breaks through gravity over time and loosens the connection just enough to periodically impair the connection. Aggravated perhaps by thermodynamics-lower indoor temperatures in winter where the whole connector might slightly contract just enough to interrupt connection to the Internet while still appearing as a solid connection.
Though as you are investigating, the lan 1 internal connection could also be compromised. In any case let's hope you are much closer to solving the problem!