1, what is the PG/Vg of your juice
2. where is the waiting part of your filling? Just putting juice in a carto does not mean every bit of stuffing all the way to wherever the coil is has gotten damp. I use 70pg/30vg. I fill a carto totally (totally - like at LEAST 18 drops per ml of carto capacity, popping the cap, never condom method baca\use I want to see inside, clear the air channel etc). After I finish filling and cleaning up a carto, I lay it on different sides for 15-20 minutes to make sure every bit of stuffing has a chance to absorb juice. if your juice is thicker than mine then you may need to wait a lot longer. Some people wait overnight. And some super-thick juices will never wet every part of a carto's stuffing - if you have juice like that then thin it for cartos.
3. What resistance cartos? And do you know that if you poke around in the threaded end hole you can short something in there (I did that once and then the carto was super hot)? And I do not recommend filling into the threaded end hole. That is for people who are stuck with some lame brand with glued on hard caps
I use Boge cartos, standard resistance. And I have singed exactly one, the first one I filled when I did not wait.