Thanks for reporting this issue!
It seems that multi_tensor_apply is triggering an illegal memory access (and so far the first debugging seems to point to a launch of this kernel on the wrong device). We’ll look into it.
As a workaround, you could try to use cuda:0 or (even better) the native automatic mixed precision implementation as described here.
To use native amp you would have to install the nightly binary or build from master.