Quickly creating an issue for this; proper issue summary will follow.
https://www.drupal.org/docs/8/upgrade/upgrade-using-web-browser#pre-upgr...
If the database credentials to your source database are correct, the upgrade review page will appear as illustrated in the screenshot below. This page shows a summary of the upgrade status for all installed modules on the old site.
Latest iterations use this help text instead:
The new site is missing modules corresponding to the old site's modules. Unless they are installed prior to the upgrade, configuration and/or content needed by them will not be available on your new site. Read the checklist to help decide what to do.
GitHub Issue #:
3577
Recent comments
Very possibly, I am looking at it now... Sorry I will be travelling away on that date. I will register, so I can look back
Images on Pages and Blocks not refreshing
Great news Francis. I'm glad I could help. Any chance we will see you at the upcoming Backdrop Live?
Images on Pages and Blocks not refreshing
Well your second Idea seems to have done the trick! So Simple!!!!! I can use this all over the place!!! Big Hug, and Thanks a Million, @yorkshirepudding !!!
Images on Pages and Blocks not refreshing