why do ignite stacks disappear?

i finally got promoted to redlotus today and i'm trying to do the new superstring dimension that wants me to use ignite, so i brought sparkle, lantern, and sirin for ignite stacks. no matter how hard i try though the ignite disappears just as quickly as it's applied. i've had this issue before but my teams have always been able to power through anyway, but now that ive been promoted it doesn't look like that's gonna work out. is there something my character or the stage or enemy is doing that im not getting? sorry if this is a dumb question