We use a lot of asset bundles and some were built with older versions of Unity but worked fine in 5.3 with some material replacement applied - only warnings we would get is "GpuProgram creation error: shader program type is unrecognised. You might have a precompiled shader asset from an old Unity version." for some bundles. But now in 5.4 the console is full of hundreds of "Failed to load GpuProgram from binary shader data in ''. warning messages which slow the editor to a crawl which is unfortunate as we have a lot of asset bundles to update. Exactly what is this new warning caused by and does it need to throw it quite so many times in the editor?