You asked a good question. I don’t know why it is, but it works 
(I’ll change that and update the post with results) UPD: I have removed those string is null conditions and everything works fine!
As for your issue. Every time scene is restarted, all objects including price texts are being reset. So you must change them each time a scene is restarted by changing texts to global variables values (with previously saved price and currency).
I have this logic in At the beginning of the scene block:
*I’m sorry I didn’t leave the screenshot in my 1st post.