Date & Time: every x min card not triggering?

Make sure the “blind” time is caused by the trigger, because maybe it’s caused by the notification card(s) you use (!).

Timeline- and push notifications can be subject to rate limits (without any warning) →
To catch this limit, in Advanced Flow you’d add a card to the error output of just one random Timeline card, and to one of each Push notification card type.
Log cards of the Simple Log app are great to use for this, and I use Signal and Telegram (as part of the CallmeBot WhatsApp, Signal, Telegram, Facebook messenger app) flow cards to report stuff.

No.
But I’m experiencing unpredictable flakiness in Sun cards of that department.