Thanks for your support.
Legacy database was synced before, yes. Checked also in the web client, but there the same issue appeared. Also, the initial download should have ended by now, we're quite some days later, laptop was restarted also several times, issue appeared also onto other devices.
In the meantime I found out that my tablet (luckily not used the last days) did not synced with Evernote yet, so I turned off all connections and the missing notes and content was still showing on the tablet. Then I duplicated those notes/content and was able to recover the missing notes and data 😉 (at least the ones I'm aware off).
FYI : One of the notes with content that partially disappeared, showed 'no date' (see att), which is also awkward imo.
Anyway, due to not syncing, i have my notes and content now back.
Thanks to you both for your kind support ! 👍🏻