By default, dataflow blocks do not propagate completion. This is by design; dataflows can represent any kind of mesh, including splits, joins, and loops (not just pipelines).
There is a PropagateCompletion
option you can set when linking that will propagate completion.
readFilesBlock.LinkTo(storeFilesInBagAction, new DataflowLinkOptions
{
PropagateCompletion = true,
});