I managed to fix it myself.. turns out that at that specific step, Vao Sai-Fuang updates your mission, and then gives you two seperate missions (one for Shadow Runners chief, one for Hazamanz of the Dead Seed chief), and my mission list was too full.
Talking to the chief for the missing mission restored that mission to my list, so all seems well now.
Talking to the chief for the missing mission restored that mission to my list, so all seems well now.
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