What triggers the missing yellow sigil in the Talos Principle?

The mentioned QR-code is indeed in the game as:

I don't have enough yellow sigils for the device I need! This is crazy!
-- Sheep v69.1.0702

After digging through the game file, I cannot find the voiceover file that you mentioned. I also can't find any mention of this in the script files, but not everything seems to be in readable lua files. What I do know is that there is no way to "finish" a level without picking up the sigil. Solving the puzzle and then exiting without picking up the sigil will just be recorded as a "puzzle exit" event, which means that the sigil will be there even after reloading the world.

There are 9 yellow sigils in levels A-1 to A-4, and 14 yellow sigils in levels B-1 to B-7. That makes a total of 23 sigils.

There are exactly 23 sigils needed to unlock all items as shown in the following sigil puzzle solutions. You can access all previous puzzles. There is even a way to get back in the tutorial area if you are quick about it.

(source: https://www.gamefaqs.com/pc/805905-the-talos-principle/faqs/70787?page=3)

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While thinking about this there might be one other problem: You unlocked the items in the "wrong" order, preventing you from completing the other yellow puzzles. The yellow puzzles you could not complete should however not be crossed out.

• A1: No requirements for 2 sigils
• A2: No requirements for 1 sigil
• A3: No requirements for 2 sigils
• A4: Connector for 4 sigils
• B1: Connector for 3 sigils, Hex for 2 sigils
• B2: Fan + hex for 1 sigil, Connector for 1 sigil, Fan + hex + connector for 1 sigil
• B3: Fan + hex for 1 sigil, Fan + hex + connector for 1 sigil
• B6: Connector for 2 sigils
• B7: Connector for 1 sigil, Hex for 1 sigil

You get 5 sigils for free. If you spend 3 sigils on the connector, do all 10 sigil puzzles with the connector, then "buy" the fan and the recorder, you end up with 2 sigils and no more yellow puzzles you can complete. I am not sure if this is possible, because I am not sure if you can access World B without access to the hexahedron. Still, if there is a way to trigger this message, then this is the most likely theory how to do it. Another way might be by buying the platform before the fan, locking you out of 4 puzzles. Again, I am not sure if you can access World C without buying the fan.

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