Your sprouts on your picture is from the root stock. You can tell by the three leaves. My guess is that your soil is too dense and you have root rot from over watering. If your graft is still alive you should repot into 511 soil or gritty mix immediately which you can lookup on garden web usually under container growing. Your graft is still alive if it is still green. Good luck. Van

Thanks, I'll change up the soil.

Would this explain the sprouts from the root stock growing well, but the sprouts from the graft dying? From the picture, the one dying sprout is from the graft.

No, if the root system is failing, both of the growth should be going down. You got vigorous growth from root stock; means the roots are 90% fine. Anyways, change the soil to a well draining one.

What comes to graft die-back, I'll let others answer to that.

Did your plants get exposed to cold temps by chance? During one of the week long warm spells in Feb, I had all my plants out. They got a tad "burned" by cold winds, even though the temps on my weather station only registered 35 as the low. The leaves looked like that and I had some die back on lots of tips. They've been pushing out new growth for the last few weeks.

They have been indoors since before the first frost. They are by the window, and I have a lamp on them. I did spray insecticide soap before bringing the plants in due to a mealy bug infestation.

Did you soap with either sun/lamp exposure before fully drying? Depending on the content of the soap mixture, that may have burned the leaves, though, the discoloration in the leaves doesn't look like surface burn from oil.

I just sprayed the soap in full sun. I dont think there was a warning on the bottle not to. But I'll keep that in mind.

Changed out the soil, so hopefully that will solve it. It was quite dense and wet.