It seems to work correctly in the Material preview, but the blend is not applied in viewport.

TO REPRODUCE:
1) Add a base Box (BOX_001)
2) From MEDIA > MATERIAL > SUBSTANCE SUPER TOOL apply RL_PBR_A-B_Blend on the Box
3) Scroll to MODIFY > MATERIAL > SUBSTANCE and change the BASE COLOR texture on the BETA panel
4) Move forward some frames (eg. 100) and change the BLEND value from -1.00 to +1.00
5) Keyframes are created correctly and the material is showing the change in the MODIFY > MATERIAL > TEXTURE SETTINGS panel, but the effect doesn't show on the object in the viewport

DISCLAIMER: I downloaded the most recent/updated version of the plugin directly from the store before testing.