Links in articles are only differentiated from the surrounding text by color, thus they can be hard to distinguish for color blind people. While most color-blind won’t have a problem with blue and total monochromacy is rare in population, it does exists. WCAG 1.4.1 mandates that Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. The shade of grey when converted to grayscale is still a bit different between links and surrounding text, but the ratio is small, as can be seen on the attached image. Given the variety of eye diseases and the fact that they often come in combination of several symptoms, this is not sufficient.
One way to fix this would be to add an “Underline links” option into the apps Settings (perhaps under an "Accessibility" section). Another option would be to underline by default in some non-obtrusive way.