So, possibly found a workaround for the time being, although I've had "fixes" before that turned out not to work after a day or so.

I underclocked my GPU by 15 mHz using MSI Afterburner. After doing that, my game has remained stable all day in normal gameplay, to include crowded, graphically busy areas like the Southern Front which were previously reliably causing the DirectX 11 error messages and subsequent crashes.

I'll continue to monitor the performance for a few days. And even if it does resolve the issue for me, I believe that this should still be treated as a problem by SE that should be fixed. There is something inherently wrong with the game if some users are forced to underclock their GPU in order to keep the program up and running. Just to be clear, it was not overclocked before, I am now running the GPU at 15 mHz below the standard specs.

I'll reply to this post again either if the DirectX 11 crashes occur again, or it remains stable for a couple of days with heavy use, whichever comes first.