This is for Self-Hosted sites Only!
Before we get our hands dirty, Self-hosted sites can be intimidating especially when having to enter a piece of code to make certain wonders work.
I searched hi and low for this one. I read in WorPress forums where and Engineer commented that they decided to eliminate the access to StumbleUpon Sharing button due to that many WorPress users are using and or have been converted to the Https URL format from Http. You can read for yourself if you like. here: https://en.forums.wordpress.com/topic/stumbleupon-sharing-button-disappeared?replies=21
First some facts, did you know that Ebay owned StumbleUpon at one time. I just found that this minute.
StumbleUpon was owned by eBay from May 2007, when it was acquired for $75 million until April 2009, when Garrett Camp, Geoff Smith and several investors bought it back. StumbleUpon is now an independent, investor-backed startup once again, with offices in San Francisco and New York City.
On to the links to hopefully provide a cure.
Since I am techy person details are the name of the game like real journalist used to be at one time.
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I hope everyone has a nice day!