Wireguard interface disappears when wan goes down

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@boredhominid

A while ago I had an unstable dsl link and while I was trying to figure it out I settled on that value, it's rather arbitrary.

I had issues earlier with incorrect mtu, so I would suggest to calculate the mtu and set that value. In linux ping use -M do
The same applies for the wg mtu.
As a test, try to disable the sqm and check if it occurs.