In developing a relatively simple scene, I noticed that detail from normal maps were not being displayed for some objects. All of the maps were generated from Substance painter as .png (16-bits max). Further investigation in the console showed that loading the normal maps was being skipped due to a float image limit of 5 textures.
Through Google, I found bug report T37264 which indicated that this was due to a limitation in CUDA. Indeed, switching the render from GPU to CPU cleared the problem (even in the viewport render, which was surprising). Also, the problem went away by using .jpg for the normal map textures.
So, my questions are: Are these steps the only solution for this problem? I was not aware that I was even using float textures. Is .png acutally a floating point format? What about the other .png maps used for color data--are they also count against the floating point texture limit?
Edit to add: I found that 8-channel .png works ok, so I guess that would be my lossless solution.