Yes, the #media do underreport some terrorist attacks.
▻https://www.washingtonpost.com/news/monkey-cage/wp/2017/03/13/yes-the-media-do-underreport-some-terrorist-attacks-just-not-the-one
But even controlling for all this [target type, fatalities, and being arrested], attacks by a Muslim perpetrator get, on average, about 4½ times more coverage.