502 Bad Gateway on preview mode - Running in local instance,.. again unexpected twist

Hi again,
I’ve been experiencing some strange trouble with the “502 Bad Gateway” in preview mode

After the adjustment that morrigan sugested previously, my local kobo instance runs well specifically, the preview mode works fine.

But the day after that i needed to run the kobo in another location without internet, Main functionalities seems ok, but when i try to edit/live-check my forms using the preview mode, the 502 Error message appears again!!

Today 've tried again. Once with internet collection and a second time without internet. Same results: 1) Preview mode OK while connected to internet 2) Preview mode “502 Bad gateway” while offline.

Does anyone have any ideas what could be causing this strange trouble?
I will appreciate greatly any suggestion.

Best regards