So the Designer freezes while opening in Safari for me. I have tried on multiple computers in normal (emptied cache) and private browsing over the last couple of days and get the same result.
Safari Version 10.1.2 (10603.3.8)
I am not super savvy with the dev tools but have attached all the errors I could see below
Thanks so much for reporting this issue you’re seeing with the Designer and Safari. This may be happening due to Safari not being up to date. I notice you’re using 10.1.2, but the current version is 12.1.2.
Is there any way you can update Safari and then try loading the Designer again? Thanks so much!