let’s dissect this one issue at at time. If I read your question correctly you’ve created install media, for both signed and unsigned distros.
With Secure boot enabled signed distros boot and unsigned behave as expected, signed boot, unsigned do not.
Wiht Secure boot disabled signed distros behave as expected (they boot) but unsigned do not behave as expected and crash during boot. The expected behavior is that both the signed and unsigned distros should boot with Secure boot disabled.
Considering the signed distros are working as expected lets not deal with them, but rather isolate the unsigned distor, and lets make sure there is nothing wrong with the actual boot media. I would reformat the USB drive and reinstall Ventory on it, that will make sure there is nothing wrong with the it. I would then redownload the Debian and Arch ISOs and validate the checksums. Copy them to the USB and again recheck the checksum to make sure they copied correctly. With Secure boot disabled I would try and boot again with either again. The expected result is that Arch (or Debian) should boot fine from Ventory with Secure boot disabled but fail with it enabled.