Check your Settings in Untapped. “Show Rating Comments” should be checked. If this is done and you still can’t see them, restarting Untapped and MtGA should fix it.
If you're on macOS and playing Premier Draft or Traditional Draft, there is a deficiency in the MTGA log system that prevents us from knowing which cards are in your pack. This prevents us from showing draft comments in that case.
While this used to work in older versions of the game, the functionality was inexplicably removed again by Wizards of the Coast. We are looking at possible workarounds here, but for the time being comments are only available in QuickDraft or on Windows.