Why does this keep happening to me?

Okay so I've been noticing for the past few hours that whenever I go onto instagram and try and watch a video and I press play for the video, the video plays, but there isn't any sound. It has the bar thing in the top left corner when there isn't any sound. I have to switch the ringer back and forth for the sound to come on for that video only and if I want to watch another video, I have to do it again. I've only had this phone for a few months. It's an iPhone 5c. Is it a glitch with instagram? What do you think the problem is? This only is an issue with instragram. If I listen to music thru the music app or youtube, it's completely fine. So answer this: do you know any reasons why it could be happening and how do I fix it? Thanks.

by the way I tried using headphones to see if it worked but it didn't:/

It's not Instagram that's acting up. It's your device. You may want to contact Apple about this issue. Hope you didn't jailbreak your device 'cause you'll need your iPhone's warranty!

Did you think of restarting the device?

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