I think that in your Custom css you have a rule that makes your block hidden.
Recently I had such a case - one of my blocks disappeared in a mobile view, after update to 4.7.9... After many analysis, I found a rule in my Custom css that I set several versions ago... After removing this rule, I have no problem with this my block.
So you review your Custom css rules, you might have a similar rule that is causing you this issue, especially rules containing "hide"
If you share a link to your site I can try to guest explore this.