I was trying to batch reproject several layers in QGIS 3.4.2 via Processing. However, after setting up my batch and clicking Run, nothing happened. Identical procedure in QGIS 2.18.26 LTR works fine.
To reproduce: Load at least two shapefiles. From Processing toolbox choose Vector General - Reproject Layer - right click Execute as Batch Process. Add the layers to the batch, choose output Path, autofill filenames and choose destination CRS. Click Run, nothing happens.
If this isn't unique to me and a bug, I'll submit a bug report.
(I just checked using a GeoTiff DEM, batch process Gdal Warp, still does not work).