half new tab (thumbnails missing over different profiles)

about https://support.mozilla.org/en-US/kb/thumbnails-new-tab-page-missing-how-get-them-back I follwed the procedure but, unfortunately, I didn't wait for the end reload page, and now I see the upper half page visible and the lower half page hidden, without frames/thumbnails visible. However, dragging the thumbnails I can see all of them 8 and I can also move them, but when released the dragging, the lower 4 frames/thumbnails again become hidden. the profile is new, I restored bookmarks and othere .json from last profile with the same issue. where am I wrong? how to resolve the problem? thanks.