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.

Recent comments
Awesome, glad I could help. ๐
Customizing Leaflet Widget popup content and appearance.
Thanks! I managed it out with your help. Turns out I had the Leaflet widget allows for a title and description. This have a dropdown menu in the Leaflet settings within the view...
Customizing Leaflet Widget popup content and appearance.
Hi geoma, no need to excuse. I think, now I got it (more or less). Your problem doesn't actually have much to do with the Leaflet module, but you struggle with the combination of...
Parent items won't show on Leaflet Widget.