I just bought 2 new Aqua D5 pumps last week and I have problems with both.

Had already 2 of them bought 3 years ago on a EK Revo Dual Serial, working perfectly fine.

I've added these other 2 on another EK Revo Dual Serial.
They are all connected to the 4 Fan inputs of the Aquaero 6 and configured as PWM.

These 2 new pumps are working, I have a flow meter and tested them one by one.

The issue with the 3rd is that the PWM range is different from the first 2.
To have it running at about 3300 rpm like the first two I have to set the min rpm at 10% instead of 35%.
Which is a bit of an issue cause ramping up it's going to end always with a different speed.

The 4th seems to just not responding to PWM.
It's basically stuck at 3700-3800 rpm and pushing like the others at full speed 4500-4800 rpm.
At 100% reports about 3700 rpm while going down to 10% the rpm goes up a little, about 3800 rpm.

Tested them on an OCTO just to double check with the same results.

Am I doomed and need to RMA them?

"This is normal. Aquacomputer uses different electronics than EKWB for the Pump, with different PWM Settings.
If you set the PWM to 0%, the Aquacomputer D5 pump will run at around 2000 rpm, while the EK D5 pumps runs a lot slower with 0% PWM."

All the D5s are from Aqua.
Only the Revo is EK, it's just a mount.
Looks more like it's wrongly calibrated, unless Aqua itself changed something in their firmware in the last 3 years.