For example, if you have a mod that gives a hat to Blue Baby (via separate png like how Maggy's wig, Cain's eyepatch, etc. works), and then you die and respawn using the Ankh, you will respawn as Blue Baby but without the hat. (Same applies with other items, as if you do this with Judas' Shadow, Dark Judas will not have whatever extra head cosmetics you give him if you modded that, and I assume the same thing will likely occur with The Lost as well if you respawn using the Missing Poster.)
I'm not sure if this occurs if you were already that character prior to reviving, but I know if you were playing a different character before you respawn as them, this issue occurs.
For example, if you have a mod that gives a hat to Blue Baby (via separate png like how Maggy's wig, Cain's eyepatch, etc. works), and then you die and respawn using the Ankh, you will respawn as Blue Baby but without the hat. (Same applies with other items, as if you do this with Judas' Shadow, Dark Judas will not have whatever extra head cosmetics you give him if you modded that, and I assume the same thing will likely occur with The Lost as well if you respawn using the Missing Poster.)
I'm not sure if this occurs if you were already that character prior to reviving, but I know if you were playing a different character before you respawn as them, this issue occurs.