Hot-melt, which seems to be how components are mounted is great for home projects, not too great if you are shipping things.
I can only see one half of the cores, in your pictures, the part outside the coil. What does the other side look like specifically is there a large gap or a small gap?
Looking at the one where the epoxy is separating, it looks like a fairly thick layer of epoxy. The issues is the inductance changes, significantly, by the total gap size. Get it wrong, and the inductor has changed a lot. If you know what the inductance is, then you can get it right if you have something to measure the inductance with.
I can only see one half of the cores, in your pictures, the part outside the coil. What does the other side look like specifically is there a large gap or a small gap?
Looking at the one where the epoxy is separating, it looks like a fairly thick layer of epoxy. The issues is the inductance changes, significantly, by the total gap size. Get it wrong, and the inductor has changed a lot. If you know what the inductance is, then you can get it right if you have something to measure the inductance with.