uploading via sftp and via Wifi is the most stupid idea I have ever heard. Wifi might interrupt infrequently, SFTP is non resumable format.
I have uploaded thousands of ISO files only using the datastore browser, and never had any problems... except in ESX 5.1 CU2 with a slow encryption... and aaaaaaaaalways via LAN.
And there is another particularity with Windows 10 / 2016, the ISO boot will look for a bootable operating system and will boot this, even if DVD drive is the first boot option.
So it is not possible to boot with default boot settings of the VM's bios, you must first edit the delay for bios to 2 seconds and then hit the F12 key for getting the Bios boot manager, then and only then Windows 10 / server 2016 will boot from ISO, e.g. overwriting the exisitng installation or upgrade it.