You said surge guard "Does not trip" most are self resetting where some problems exist.
One thing I have seen many times, Both in the sticks and bricks where I lived for about 30 years, and i the motor home last summer where I am parked right now.
This is where shore/mains power is lost for like 1/2 to 30 seconds, basically power goes off, and right back on, By the time I could get out the door and look at ye old LCD display it is counting down the seconds to re-connect.
and about 3 minutes after flicker.. power returns to Motor home
In my case the ATS (and this is the best kind in my not very humble opinion) the resting state (no power) is "SHORE".
The only way to get it to switch over to the Generator is to start it up.
Home is where I park it!