This might be a bit late to the party but my setup was working fine on my vWii until I connected the USB and SD into my Wii, then it didn't work on my WiiU anymore.
fortunately I had a backup which I was able to compare it to, so here is backed up meta.xml below
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<app version="1">
<name> USB Loader GX</name>
<coder>USB Loader GX Team</coder>
<version>3.0 r1281</version>
<release_date>20230107233054</release_date>
<arguments>
<arg>--ios=249</arg>
<arg>--bootios=58</arg>
<arg>--usbport=0</arg>
<arg>--mountusb=1</arg>
<arg>--sdmode=0</arg>
</arguments>
The ios had changed to 250
The usbport had changed to 2
Once I set this back it started again, it worked on my WiiU again