@Steve6443 I see your quote below from the Asus forum
Let's encrypt sends a challenge to my NAS but the response is incorrect hence the verification only goes as far as a pre certificate.
At least in your case, if you see a Precert in the log you should conclude the challenge worked and a cert was issued. There is often a delay in posting the Leaf to the log as shown by crt.sh. And, looking at crt.sh now shows your Leaf's matching those earlier Precerts (see here). You still have a more recently issued cert that crt.sh is only showing the precert but I'm sure that will post later because it is visible in censys.io (which is much harder to use).
The better conclusion for what is happening is you got a cert but your Asus system did not properly integrate it into your system.
You were able to use a different name and get that to work. That proves your system can properly request and integrate certs. Why it can't just for that one name points to an internal issue in your Asus config / software.
I know this isn't helpful for a remedy. I just hope it helps identify the root cause.