I've had two Lexar CFast cards (256GB - 3400x) die on me during shoots. They were both bought when the cards first came out ($1500 ea.).
When I was at NAB, I spoke to Lexar and informed them that many people have had issues with their cards and believed Lexar to be dead. They told me they were bought by another company and have been joining with the new owner and there is a plan to release new CFast cards in the near future. Not easy to pull off when people are not happy with your customer service and/or brand.
After I left the booth, within 15 minutes I received a phone call from their Support Department and they wanted to take care of my card issue.
Skipping to the important part, I received my two new replacement cards today (256GB - 3500x).
If anyone has issues with their cards:
http://www.lexar.com/supportNote: They do have requirements to show proof of purchase, etc.