Hmm wondering if it's Lexar related or 200 gig related.
Did a quick google on the issue and got this back :-
Before using a microSD card (not supplied) in your Walkman for the first time, be sure to format the microSD card using the Walkman by following the steps below. Formatting a microSD card will delete all data stored on the microSD card, so be careful not to delete important data.
- From the Home menu, select [SD Card Settings].
- Select [Format SD Card] - [Yes]. All data stored on the microSD card is deleted.
Note
Be sure to format the microSD card using your Walkman when you use it on the Walkman for the first time"
Bit of a shame if that is the issue. Does any of your other cards work ok?
Edit to add :-
I knew I'd seen similar issues over on the w1ma/z thread's. Headfier Crafty Clown found this program "https://www.sdcard.org/downloads/formatter_4/index.html" which seemed to help him. For what it's worth below is his original post :-
It seems like the new Sony WM devices are very fussy when it comes to the formatting of cards.
"Three of my cards; 1 x 128gig card and 2 x 200gig cards would not work, whatever way I tried formatting them on several different Windows 10 machines.
I did a bit of research and came across some software from the SD association, who advice using a dedicated formatting tool for SD cards rather than OS formatting.
Long story short I downloaded the software, used it on all three cards and they all now work perfectly.
Here's a link if anyone else is struggling with an SD card that can't be recognised
https://www.sdcard.org/downloads/formatter_4/index.htm"
No guarantees but that might be worth a shot.