Why does my mobile preview show larger fonts in random places?

Ever since the update to the UI, we've noticed that the mobile preview shows larger font size in certain areas of our weekly newsletter. In the past, we've fixed this by increasing the font of affected areas, saving it, closing the campaign then reopening it. After that we reverted the affected areas back to the original font size and the mobile preview would be fixed. This does not work anymore. Please advise. Thank you!