Brewmaster Weapons are blank

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Weapons slots are empty for Brewmaster

First obseravtion - what priority do YOU place on Brewmaster?
As your Snapshot shows, you have the following set as priority:

DPS > Healer > Tank
In the Optimiser that matters - if it’s not set correctly, the optimiser will show errant results.

That said, I clicked “Unlock All” & weapons ‘appeared’, despite any seeming to have been locked to Brewmaster.

Yeah somehow bad weapon locks got in place for your Brewmaster spec… I’m trying to figure out how that happened. It has a 2-hander locked in the main-hand and a 1-hander locked in the off-hand, which is not possible, so it has no choice but to blank/skip the weapon slots.

Pressing “Unlock All” for your Brewmaster spec as eighjan said will fix the issue for now, and I’ll try to figure out how an invalid set of locks made its way into your settings in the first place – theoretically the UI should prevent that from happening.