aha! So what happened here was that adding "the" pushed the tag over the 100 character limit, which the tagset will allow you to "add" on the edit interface, but will not show on the actual tagset selector, because it hasn't actually been added, which makes it look like the tag's been deleted. I've re-added it as "The Following: It takes longer for Ryan to figure out Joe's a killer; they get closer than in canon" to preserve both the prefix that corrals it near others in that fandom, and to keep all the parts of the original freeform. You should be able to find it in the tagset now!

Thanks for bringing this to my attention! At 104 characters long it snuck by us.