Media Encoder DPX Import Not Working

In Media Encoder I can't seem to get DPX sequences to import. Where it would normally show the DPX Sequence checkbox it just shows "Sequence Not Available" and it's greyed out. As a test I changed the extension to .PNG (not actually converting them) and the PNG Sequence option was available. This obviously won't actually work, but proves that it's specific to DPX (also tried the CIN extension).

The docs indicate it will work (https://helpx.adobe.com/in/media-encoder/using/file-formats-supported-import.html), it says "You can import files of any still-image format as a sequence. For more information, see Import items into the encoding queue."

I'm testing this on version 15.4.1, but it seems to happen in Media encoder 2020 as well.

Any ideas?