I finally found it out myself, rates including BF are OK.

Has there been any change to how long after the successful stay is completed that the 5k (previously the voucher) posts or is received by email? For me, it used to be four days after check-out.

Took 3 or 4 days for my 5k points to post.

Agoda is notorious for adjusting prices bases on click-through and cookies; do you still get the lower price when you open Agoda from a fresh browser (incognito)? I've personally never had Agoda itself have a lower price, it was always a redirect from Kayak or so. Try instructing them to do exactly as you do and maybe they'll accept the BRG.

successful non-refundable BRG claim
 

I was eyeing a Grand Hyatt located in Asia and saw that the Hyatt rates were the same as 3rd party rates - all except for the non-refundable rate. Even with the Hyatt's current 20% promo, Agoda's non-refundable prepaid rate was still about 15% less than Hyatt's non-refundable prepaid rate. However, I didn't want to actually book Hyatt's non-refundable rate, because I didn't want to be stuck with it in the event the BRG was not approved

So, what I did was I booked Hyatt's standard refundable rate which was the same as the comparable rate on Agoda. Of course, this claim was not approved. What I did then was ask Hyatt BRG to look at Agoda's non-refundable rate (knowing that it was less than Hyatt's) and told them that this is rate that I wished to book.

Before Hyatt BRG booked the non-refundable Hyatt rate, they verified that Agoda's comparable non-refundable rate was indeed less. Thus, both Hyatt BRG and I knew that this claim would be approved before even processing it.

A little while later, I received an email from Hyatt BRG confirming the successful BRG claim with a rate that was 20% less than Agoda's non-refundable rate. In the end, the net was a rate that was about 30% less than Hyatt's originally published rate. I further applied a suite upgrade.

Great strategy!

Are you saying after the original denial and conversation with Hyatt you went ahead and purchased the non-refundable rate and then filed a second claim, knowing it would be approved? Or was this all entirely orchestrated within the bounds of the original claim?

Congratulations!

I only made a single reservation. First, as mentioned, it was at the standard, refundable rate. Then, once both Hyatt BRG and I knew the claim would be approved, the same reservation was then changed to a non-refundable rate retaining the original confirmation #.

I maintained correspondence with the same BRG rep throughout the entire process so they were already familiar with what was going on. This made for a timely and seamless BRG approval.

Congratulations, but this isn't something you should expect to have happen on a regular basis.

I had no idea we could get pre-paid BRG via the back door like this...

As someone else already said, I would have ZERO confidence this is reproducible on even the smallest scale.

Is the prevailing wisdom that it is best to use the online BRG form or to call on the phone with your claim?

If you phone you'll be directed to use the form.