I noticed that the durability of my netherite soul sand 3 unbreaking 3 boots goes down very fast even on blocks that are not soul soil/sand. I was working in the nether about 1k from base, travelled down a soul soil path to get there which took about 25% durability. After about 2 hours of working in the area not on soul soil/sand the boots were nearly broken but the rest of the armour was still in good condition (all has mending) I believe this is a bug that the boots are breaking faster with soul speed 3 even when traveling on normal blocks in the nether.

I've followed this up by doing a test in the same work area with a set of boots with the same enchants minus the soul speed and they are fine compared to the ones with soul speed.