Tripwirehooks sometimes stay powered without an entity triggering the tripwire. In my case, removig and replacing the tripwirehooks one at a time sis not work: when removing and replacing one, the other one would activate without entity. I tried doing

kill e[type=!player] 

and had no success, since there were already no entieties. The glitchy tripwirehooks might have been cloned in, instead of been placed by hand. I'm not sure, because I placed some and cloned others.

In the picture you can see the tripwirehook powered and the command failing.