My site randomly goes down

I have a website built on the MERN stack, hosted on Heroku and using Hover for the domain registrar. However, my site seems to randomly just not connect. This seems to be happening randomly, although it's hard to tell. Also, my Heroku app that isn't using a custom domain loads just fine which makes me pretty sure that Heroku is not the issue. This has been happening quite frequently and the site will be down for maybe hours at a time (although I am not checking it every 5 minutes so it's hard to be 100% certain about that). And when it is up it only stays up for around 15 to 30 minutes or so.