The objective wouldn't be so bad, if the mines wouldn't randomly explode while you are disarming them, despite still having time left.
Best guess as to what causes the bug is if you fail to reach it once the timer hits 29 seconds, it will explode if you try to dismantle it.
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If it doesn't say "Disabling Mine" then it's a fake Fake mines say "Deactivating" when you cap them