Faced this today (Oct-06-2019)
I double-checked every setting, all of them, didn't fix issue for me unless I changed some content in my index.html file. I also added some files to the repo to make it "alive" but in vain.
So, In my case, I opened up my index.html right in the browser, clicked on edit and added a single word, commit to master branch, refreshed and it took less than 5 seconds and it was up again.
P.S. I tried pretty much all solutions given anywhere nothing else worked for me.