Rohloff gear can only shift between 3 and 4, even when gear disconnected from hub
Check the cables.

Rohloff classifies the gear shifter cables as a consumable.  They may wear out and need replacement over the years.  Check the gear shifter cables carefully for any damage; they might need replacement.  Be aware that they are not ordinary cables, but that you need special Rohloff gear cables to fit.

In my case, there was a damage in the gear shifter cables.  Replacement resolved the problem.