Note: untested with this mod standalone, many other mods installed.
I've found that if you're currently on slot 2 and you want to go to anywhere in slots 4-6 (tapping 2 and then 1-3), the game does not highlight slots 4-6 when you first tap 2. This sometimes happens for other combinations (e.g. currently on slot 3, want to go to slot 9 = cannot go to slots 7-9 selection.)

Will report back when I've tested in vanilla with this mod standalone as it could very well be a conflict. Just wondering if somebody knows of the issue by default and it is in the mod.

Re: above. It was a mod incompatibility. Haven't found which one it is but it's something I gotta live with in this list of mods.