A few things:
1. Deload on your barbell deadlifts and work your form. Drop down as low as you need to go so that you can work form without worrying about the weight.
2. Continue to use the hex bar for your heavy weight deadlifts.
3. Find other exercises to continue to build your lower back.
From what I can tell, people seem to think that hex bar deads are more similar to a squat in mechanics. This means that the activation in your lumbar won't be as high with hex deads as with a straight bar.
This article agrees, and sells that as a benefit: T NATION | The Trap Bar Deadlift
From that article:
and finally:Should you abandon the straight bar deadlift altogether?
It depends on the goal. If you're concerned about the risk of lower back injury, the trap bar is definitely the safer choice. However, if you're trying to achieve maximum back extensor and hamstring recruitment, then the straight bar is the better option.
Keep in mind that the hamstring's primary role will always be to bend your knee and extend your hip when you're bent forward. While this does occur during the trap bar deadlift, it's to a lesser degree than during the straight bar version, which keeps most of the load on the hip joint, rather than the knee and ankle joints.
All this research is making me want to try it out now, actually.The important thing to remember is that if you're going to truly "replace" the traditional deadlift, plan on adding a bunch of other hip-dominant exercises like glute/ham raises, kettlebell swings, hip thrusts, etc., to your program.