The online help does have a section where webfile is mention actually - although it is not much help for your case:
It might be a bug and as such it should be reported to Qlik support.
A workaround for you would be to use a proxy server to accept 443 connections and forward them to 8084.
Hello Beppe - there is an explanation to this and I have also noticed this and brought it up to our products team. I believe there is a solution in the works - but requires manual editing of the data load script - once the web file connection is created. - I have asked the product team to reply to this thread to provide the exact information - however it may be something they added in the web file connector as a patch in a future release. They will let us know more. If we don't hear form them - please reply to the post and I will be notified and follow-up.
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The problem you mentioned above was caused by a security rule set in our cloud, after discussing the issue with our security expert, we've relaxed the settings so that requests addressed to HTTPS servers listening on registered ports can pass through. The fix should be in by end of tomorrow.