Just wondering, what tyres fitted? Presume still oe? As top of the range tyres need little balancing, rarely more than 30grams. Where as a linglong I have here has nearer 130 odd and a strip of weights 6inches long.
Rim slip doesn't necessarily mean deflation. Any tyre will eventually slip if enough force is applied. Thing is within the realms of passenger cars, that amount of force should be well out of reach of insignia.
But what else could cause it?
Tyre slip. Unlikely to be factory fit related. Maybe a fault if aftermarket tyres fitted, and a faulty tyre soap used. A tyres seal could be a solution, like they used for corroded rims, to practically glue the tyre on.
Balance, as said it can't go out of balance unless an amount of volume has changed. (Unless its rim slip)
Something in the wheel. If its run flat there could be balls of rubber granules within, but that would be impossible to balance up in the first place. Loose tpms sensor perhaps? Are they a band type strapped to the wheel rim?
Ditto tyre Weld gunk.
Is it defo balanced correctly? Or is it something that taks a week or so to show up when finally a motorway trip shows the problem?
What was the error on the balancer when re checked? How far out ?