I think you were training just fine. Your LT is 84% of your max HR, that's within range.

With enough time, you probably can raise that LT to 88% or so. But it can take years to get it to that point.

There's also the possibility that the LT blood test isn't that valuable. Go out and do a functional test (see the sticky article in this forum). If you've been riding at a higher intensity than your measured LT, I suspect your actual threshold is higher.