I have a problem with grids with locked column and locking/unlocking action columns.
If I lock/unlock an action column I get :
ext-all-debug.js:234491 Uncaught TypeError: Cannot read property 'length' of undefined
at constructor.onLock (ext-all-debug.js:234491)
at constructor.lock (ext-all-debug.js:246472)
at constructor.onNodeDrop (ext-all-debug.js:230786)

After that the grid is broken

The same occurs when I move the column from locked view or to locked view with drag&drop.

Sencha fiddle to try it:
https://fiddle.sencha.com/#view/editor&fiddle/37n7