This is similar to the issue that I mentioned in the [Bug] ## added at the beginning of a sentence after editing it topic.
From what I have been able to tell, it happens for any text in LingQ that appears in brackets: […]
If you have an Ipad/Android phone (what I have experience with using LingQ), you might be able to go and manually delete the slashes like I do—until LingQ can fix the bug.