How to debug: ping "Name or service not known" with Ubuntu 20.04 in WSL1 in Windows 10, even with required nameserev settings for VPN?

I'm running into a tough problem: With VPN for my employer's intranet, I cannot ping to a host "sensor-access01" on the Intranet. The same command:

ping sensor-access01

works in Windows CMD console with the expected replies:

Pinging sensor-access01.xxx.domain [10.1.242.50] with 32 bytes of data:
Reply from 10.1.242.50: bytes=32 time=13ms TTL=62

but in the Ubuntu/WSL I only got the error:

ping: sensor-access01: Name or service not known

I have made sure that the content of /etc/resolv.conf in the Ubuntu has the correct nameserves for the VPN, following the solution at WSL - DNS not working when connected to VPN by Donatello and I confirmed that the content of /etc/resolv.conf changes accordingly with the presence and absence of the VPN

I'm seeking advice to troubleshoot for a solution.

Here are a few potential suspicions.

1. The Ubuntu 20.04 was supposed to be installed with WSL2, as the version of my Windows 10 supports WSL2, but I checked that it WSL2 was not enabled due to some reason that I don't quite know. Could it be possible, due to the inconsistent version of WSL? (expected vs. the actually used), the Ubuntu does not work properly? (I had Ubuntu/WSL1 with an older machine/Windows 10, I had no issue with DNS/ping. This new Ubuntu installation otherwise has no problem found so far.)
2. The host that I cannot ping is a host on the Intranet, for other host, such as dropbox.com, I'm able to get host address resolution without the name error in the same Ubuntu and same VPN. I still cannot ping dropbox.com, but I guess that it might be a separate issue with the Intranet policy. Here is the different response:

ping dropbox.com

PING dropbox.com (162.125.248.18) 56(84) bytes of data.

^C

--- dropbox.com ping statistics ---

8 packets transmitted, 0 received, 100% packet loss, time 7007ms