I have this issue too.
I completed the original (Legacy) Essentials a few years back, and went on to do some of the Junior Programmers pathway. I dropped learning Unity, but have come back, and wanted to try out the new version Unity Essentials as a refresher, using Unity 6.
I started the pathway, then shifted to the In-Editor version, then quickly shifted back as I preferred to use the browser version on a second screen.
I completed Mission 1, did the quiz and moved onto Mission 2, but even though all parts of Mission 1 are marked as complete, it’s still saying 0/6 missions, and the button says ‘Start Pathway’, much as in the OP’s screenshot. Even if I carry on, it still says ‘Start Pathway’.
However, the In-Editor version’s button says ‘Resume Pathway’!
I thought it might be a browser issue (I use Firefox on both Windows and Mac) but it has the same issue in other browsers I tried, so must be a backend database issue.
There were the same problems. Tutorials are counted only for a specific version. Try to complete it on other versions of the tutorial.