Not sure what exact time your enthusiasm updates, but if you TIE'd every game leading up to the Thursday cup game which you PON'd (so the same as TIE), your enthusiasm should have been as follows, according to the model that has never been wrong for me in ten seasons.
Friday, June 3rd: 13.4
Sat, after your game: 15.9
Sun, after update: 13.7
Mon, after update: 12.2
Tues, after your game: 14.7
Weds, after the day's update: 12.9
Thurs, after your PON Cup Semi: 15.5
Friday, after update: 13.4
So, if X was measured before the update on Wednesday, you'd have fallen from 14.7 to 13.4, which would look like 15 to 13 with rounding. If it was for after the update on Wednesday, then something indeed seems amiss.