I have had this problem on both Google Chrome and Firefox, on my current laptop (Windows 10) and my previous laptop (also Windows 10) and I have also experienced it on different wifi networks, not just my home network. I've been experiencing a persistent issue with Tumblr where videos will not load or play, or may stop loading after a few seconds. If the videos stop playing on tumblr, they also stop playing on any other website (eg: youtube) I'm on at the same time, even if it's in a different tab, window or even a different browser. It doesn't seem to be an issue if I'm not on Tumblr. Usually waiting several minutes until it fixes itself or refreshing every single tab seems to be the only way to get it going again. When I'm on Tumblr I tend to have several tabs open on different pages at the same time, so I'm not sure if this contributes to the issue.