Cannot edit part of mesh

Hello everyone.

I’ve got problem with my model mesh. After toying with armatures for few hours I’ve noticed that part of my mesh won’t animate. When checked it happened that on some faces I cannot aply any transform. I can delete faulty faces but cannot select edges near them so I can’t replace them with filling with new ones.

As you can see faulty and correct faces are within one object data.

I would be very glad if for any help.

Best regards