Make sure these things are in place, and it should work:

1) - Have the secretregiontrigger in place, and being both sufficiently below ground and above what ever should be hidden.

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2) - The trigger needs to know it's locked. Put "LockSecretRegion(TRIGGERGUID_SecretRegionTrigger_000_117f85c7-0f28-4636-a01b-5c3ddb614853);" in the INIT section.

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3) - Make the hidden region unlock after an event of your choice, in my example case after clicking the "Rabbit Goes Boom Lever". Yes, I like exploding rabbits.

Add this under THEN in KB section.
"UnlockSecretRegion(TRIGGERGUID_SecretRegionTrigger_000_117f85c7-0f28-4636-a01b-5c3ddb614853);"
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4) - And likely the missing cause in your case, open Level > Level Data and make sure "Hide Shroud" is set to 'False'.

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Then it should work.

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