Hi HeroicJay, I am happy to report that Weapon Unleash was indeed the issue!
I first tried going back to that old project that I mentioned in my first post and disabling it just to see if it works, and it ran perfectly. This also means that the plugin is compatible with everything else I had (in that project, I also had some plugins from SRD, Caethyril, Alistair Engine, Galv, Ramza, Toby Tasha, YoraeRasante, Turran, and some commissioned ones from Trihan that I have recently asked him to release publicly after testing them). In other words, the only compatibility issue was with Weapon Unleash, at least out of the plugins I had.
I will just work around it, as I was mostly using it in conjunction with Target Core and Row Formation to determine how far back a weapon's range is for the attacking battler (e.g., Bow users can attack from Row 3 but not Sword users), but I am already applying a JS to the other physical skills that are shared, so Weapon Unleash was just a convenience tool rather than a necessity.
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Wow, I actually found Weapon Unleash in a download from ages ago, and the issue is not even close to anything I expected. In essence, it's a... bug? maybe? in Weapon Unleash that may or may not affect things normally (still piecing this mess together), and to be honest, I'm a little surprised it works when Dualtechs ISN'T installed.
I'm still piecing things together, but the Dualtech is being resolved when it isn't supposed to be. Actually, I'm not even sure it's necessarily Weapon Unleash that has it wrong, but something isn't communicating correctly with other things.
EDIT: I'm understanding a little better what's going on here, and... I'm not actually sure it's a bug in Weapon Unleash OR Dualtechs individually, but it's certainly a weird interaction when both are together.