Critical issue with updating to Sydney 1.8.5 / no content will be shown

Hello,
I am using Sydney free theme for a small project for years and all works great.
I am using Sydney 1.5.3

But now I have got two issues, one is very urgent, beacuse the website did not show any content after updating.

Today I have updated all (WordPress, Plugins and Sydney).

I have got two issues after updating.
1.) Updating Sydney Toolbox will crash the whole site, no access to page and wp-admin. I have deactivated and deinstalled the Sydney toolbox, now the page will work again. Sydney toolbox will not be used, so I can do this. But how to fix this if the Toolbox will be used in future?

2.) This is the most important issue of the both issues. After updating Sydney from 1.5.3 to 1.8.5 the page will be loaded and is scrollable but there is no content, no text, no header, no images…nothing. The only element which will be shown are the two red small circles which are shown while the side is loading. After updating there was a Info box to deside which header I want to use, the new or the old one. I have decided to the old one and in an other try we have not choosed one of them. But the issue is the same…no content will be shown.

How to solve this?

kind regards