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
You might be on to something there.
Until now, I have been running Claymore 15, in ethOS, but also tried ethminer, no difference.