UM Welcome not working in UM 17.10 beta 1 32 bit

[tomi]

This post is not 17.10 specific but there could be something in it that could be of use:

Welcome not working on Mac PPC 16.04

A recent update installed Welcome for 17.10 on my Mac PPC running 16.04. It no longer works. I get a white screen. Clicking on the white screen yields a black screen. Is there any way to return to Welcome for 16.04?