Q1: What does "When Digivolving effects don't activate" mean, exactly?

This effect prevents When Digivolving effects on cards from activating. When Digivolving effects can no longer activate by triggering or when effects such as "activate that card's When Digivolving" effect" activate.

Q2: I used a card affected by "can't activate When Digivolving effects" to attack. Can I activate that card's When Digivolving When Attacking effect at such times?

Yes, you can. The effect can activate if it activates upon the When Attacking timing.

Q3: If a card is affected by "can't activate When Digivolving effects," can other effects activate its When Digivolving effect?

No, it can't be activated.

Q4: If a card is affected by "can't activate When Digivolving effects," can I process just the "by" condition in its When Digivolving effect?

No, you can't.

Q5: A card that was given "can't activate When Digivolving effects" digivolved into a card that has a When Digivolving When Attacking Once Per Turn effect. Does that count as an instance of that effect's X Per Turn even if that effect can't be activated upon the timing when that card digivolved?

No, it doesn't count. The effect can't activate upon the When Digivolving timing, therefore it doesn't count as an instance of that effect's X Per Turn.

Q6: What happens to cards placed face up in the security stack by effects?

They become face-up security cards that remain revealed. Other than rules that specify face-up security cards, the rules apply in the same manner as standard security cards.

Q7: What happens upon a security check for a security card that is placed face-up?

The check is performed with the card left revealed. Other than rules for cards left revealed, the rules apply in the same manner as standard security checks.

Q8: Does a card's Security effect trigger upon a security check with that card placed face-up?

Yes, it triggers.

Q9: What happens if I shuffle a security stack that includes security cards placed face-up?

Any face-up cards are placed face down, then you shuffle the cards. After shuffling, all cards are left face-down.