Salient Child Theme and new Visual Composer

My Salient Child Theme has been running since 2016 and is now version 8. A Visual Composer was integrated but not a plugin in this version. As a result of downloading the new Visual Composer (VC), the old and new version co-exist. The problem is that all 80 subpages are compatible with the old VC, whose text fields are now only shown in white colored letters and HTML. As a result, at first glance they appear empty. After downloading the new VC, the old VC was already functioning with the old text fields in normal black letters but for some reason, it does not work anymore and editing is close to impossible. Also, the loading time after saving changes is very long and the whole system performance has significantly slowed down. Any advice what I can do ? Thanks so much!