Ethminer stopped working for my 4gb cards this morning as well.  And my rigs with 8gb cards are still working fine. 

I run ubuntu 18.04 no custom OS.  And Claymore v15 still works on the 4gb cards.

Must be some code issue with how ethminer handles buffer allocation

cl 16:56:55 cl-1     Build info success:
cl 16:56:55 cl-1     Creating light cache buffer, size: 60.00 MB
cl 16:56:55 cl-1     Creating DAG buffer, size: 3.75 GB, free: 190.37 MB
 X 16:56:55 cl-1     Creating DAG buffer failed: clCreateBuffer: CL_INVALID_BUFFER_SIZE (-61)
SIGSEGV encountered ...


I bet ethOS runs ethminer as well