i have seen this occasionally happen, though not in solo play

ive seen it happen in duos when you wipe, and one person is still the "rez ghost" while the other is normal and accidentally starts the fight

when the other players rez ghost ends it resets the fight and costs another thread

looking at your video, it looks like it might be the same/similar issue except it is being caused by your tomeshell verse

the tomeshell popped off its aoe right as you rezzed and was in range to hit the boss (even though that aoe does no dmg and just applies minor mangle), but you were still a rez ghost when that happened so it triggered another fight reset

its kind of annoying, but slightly different issue than some other extra thread losses, not sure if this is something that will be fixed in the next release as i did see some stuff in patch notes about archive fixes for some issues (though mostly stuck mobs)