It would be nice to have the same implementation as in kate: Using Shortcuts -> Standard Shortcuts -> Activate Next/Previous Tab it is possible to navigate each view in split view separately. (Using splitview "Most-Recently-Used Document Switcher" does not cycle tabs in each view separately.)
Either I didn' find how to do this in 5.5 or it has been implemented since. With kdevelop 5.9 this can be configured in Settings -> Configure Keyboard Shortcuts...: Switch tab inside split view: Shortcuts -> KDevelop -> Next Window (default: Alt+Shift+right) Shortcuts -> KDevelop -> Previous Window (default: Alt+Shift+left) Switch split views: Shortcuts -> KDevelop -> Next Split View (default: Ctrl+Shift+N) Shortcuts -> KDevelop -> Previous Split View (default: Ctrl+Shift+P)