I think this is a bug. I have a m2 Mac and when I create a custom block to use in builder, builder runs fine and strategies are created, but when I go to look at the codes, I cannot view them because of this error. I've tried figuring this out on my own with no success and now assume it is a bug. I'll upload some screenshots of the error and the system I was using with the custom block.
Status changed from New to Fixed
Attachment image-0.png added
Attachment str_fixed.sqx added
It is already fixed in RC4, please download it from our home page.
I have also fixed your corrupted strategy file, it is attached.