Could not determine UDID error if installed via AltStore PAL

[Sab44]

I have installed AltStore Classic via AltStore PAL. AltServer is running on a Windows machine and connected to AltStore wirelessly via iTunes. Manual app refresh is successful 100% each time. But background refresh very often fails with:

AltStore.OperationError 1006 AltStore could not determine this device's UDID.

Sometimes background refresh will work though. It feels like once I do a manual refresh the error doesn’t appear for a while, but once it happens it will keep popping up.