Thanks a lot for the answer! By your suggestions, I compiled a debug build, attached the debugger and I found that it was the following assert in VkCommandBuffer.cpp that failed:
ASSERT(offset + size <= vk::MAX_PUSH_CONSTANT_SIZE);
My push constant block is 208 bytes which is greater than MAX_PUSH_CONSTANT_SIZE==128. This is indeed according to the spec, but apparently NVIDIA is using a larger value. Still, an error return code or some other orderly failure would be nicer than the silent shutdown of the ASSERT.
For my part, I'll just rewrite my code to use a uniform instead of the push constant and I'll probably be good to go.