For information this is called "uncollected funds" rather than "insufficient funds", and the stories are consistent. I think you have a legitimate grievance with your bank, not for holding the funds, but for showing them as available before they cleared. They should speak with American Express on your behalf.
Nonetheless, American Express has seen that you depend on reimbursements to pay, and may well question why your employer is expecting you to layout money on this scale.
=/ Well I just got off the phone with amex, paid off the card, moved all my MR points to airline miles. And was told that despite being paid off, they cant re-open my account and i would have to apply for a new one. which i dont think ill do. I've gotten a number of calls from amex over the past couple months asking about my charges, each time ive explained to them that they are business charges, and each time they have been satisfied with me. If they had said not to charge so much, or only use it for personal charges, id have been fine with that. Just seems dumb to me that they would cancel me totally over a snafu with the bank even when they STILL got all their money.