You may be stuck between the rock and the proverbial hard place.
While there's indication it could well be a software issue (ie driver filters and perhaps also the apps they support), IMO still can't rule out hardware.
Problem is: even if it's the Dell and/or the ST Micro driver filters interfering with your Lexar... I'm guessing you still need them for the features they support: Disk Encryption and Free Fall protection
I had a similar h/w vs s/w issue once. What I did: Take the laptop to a local computer store, tell them you want a secure flash drive you can verify works with your Dell. If it works, you'll buy the flash. Otherwise, you'd be returning it. In which case, they should let you try one in the store to check it out and saves you and them the hassle of the return
Plus, if another vendor secure flash works, you're good to go. If NOT, you can go yell at Dell!