The example below is created as Point Text, not a Paragraph Text, so there aren't any bounding boxes. Usually if the bounding box is not big enough, the whole word will disappear, not just one or two characters. Bounding box is not an issue, as this happens as this will happen no only the LAST characters, but the FIRST characters of a text layer.
Characters in a text layer will disappear and reappear on a whim and there's nothing that I've been able to troubleshoot that has helped. Since updating to Photoshop CC 2015.5, I have encountered many challenges in having text appear properly for me.