Just brought a wingnut and there is 4 adjustment straps which move very easily.
I’m thinking safety pins but don’t fancy being stabbed if one comes undone.

Can they be looped back through the adjusters?

Rubber bands or O-rings round the the straps after they go through the buckle?

Not familiar with wingnut pack, but do they have ladder locks? They should be secure if threaded properly if they aren’t they are useless.

can you just loosely knot the strap where it goes into the buckle/adjuster

or get a nappy pin (safety pin with an extra sliding head cover that goes over the clip in end)

I knot mine just under the buckle thingy, there’s normally more than enough strap spare to do this. If the knot digs into a shoulder or pressure point then I use a couple of large stitches with a decent thick cotton/twine but to use this method means its at a fixed point and you are happy where the rucksack sits, which as we know isn’t always in the same place on your back when loaded with different things.

Not fit for purpose and refund ?