Erosion follows the same wind
The exposure that works a dock also works the bank behind it. Wave energy arriving day after day removes material at the waterline, and because the loss is gradual it is usually noticed as a change in the shape of the yard rather than as damage.
Undercutting is invisible until it is not
The failure mode that matters is material being removed from beneath a wall or bank while the surface above still looks intact. By the time there is a visible slump, the void has usually been developing for a long time.
Drawdown is the inspection window
When the lake is low, the base of a wall and the toe of a bank are visible and reachable. That is the only time of year the relevant part can actually be assessed, which makes winter the right season to ask the question rather than the spring.