Hello.
I've always used the Utility to install Rockbox on my Clip Zip and never had any trouble, last time I updated was a year ago and it worked perfectly, however this new version gets stuck on the bootloader installation.
Here's the error log in case it's of any help;
https://pastebin.com/m1bJhv3KI had to dig up Rockbox Utility v1.4.1 from a personal backup to be able to install the bootloader again. I'm aware you only need to do that once, but I flashed stock firmware because other person that wasn't familiar with Rockbox was using it for a while, also because it seems that stock had better FM reception, for some reason.
Cheers.