[Ryuji]

This paper material has an in-camera speed of ISO 25 which is what the Ilford MGIV has under identical conditions.

I disagree. Ilford MG4 has very much lower than that speed, more like 2.5 or lower, if you measure it as a negative emulsion. Of course, one of the problems is to develop the emulsion to a g-bar of 0.62 but even if you accept 2 or so, the speed is still very low.

But bromide emulsion should be easily capable of 25 speed.

In particular, your raw and digested emulsions look quite a bit lower contrast compared to MG4 with monochromatic green light, so it should help you in getting speed above 25.

Also, I don't know which dye you used (it doesn't show J-aggregate so it's not the ones used for color films), but it doesn't exhibit much desensitization with extra dye, so I suspect you added quite a bit of iodide, or made it core-shell?

Finally, do you have a color scan of the test prints?