download zip distribution Win81SE works fine here.
currently tested with Win8.1SE_2016-12-23.zip
download or update Win81SE from server works fine here.
Following other topic,
If you have Win10PESE,
On builder See:
>> Utils\"Download Other Projects"
Follow 3 step instructions with "Win8.1SE" button,
This will get you up to date "Win8.1SE" from server.