Never had this problem myself. Run these tyres for over 10 000kms so far (up to 110 km/hr) without any issues at all. Maybe it's mechanical - alignment or balancing?

Get your wheels balanced mate

The legal minimum is 1.7 mm I think but I would replace them when they got down to 3.2 mm (1/8 inch) Your tyres are the only thing between you and the road and a big tree. In my opinion anything less than 3 mm is dangerous on a wet road.

Deflated to around 18 or 20 PSI they are similar to most other AT tyres on a beach. It largely depends on how the vehicle is driven. I think most tyre purchases involve some compromise. The best tyre in sand would be an aircraft type - plain round like a doughnut with very little tread but good for nothing else.