Premiere Pro Beta v27 H.264 elementary-stream export is broken when Multiplexer is set to None.

Premiere Pro Beta v27 is having a consistent H.264 export issue related to the Multiplexer setting.

When I export using H.264 with Multiplexer set to MP4, Premiere does not properly combine the video and audio into a single MP4 file and instead exports the video and audio separately.

When I change Multiplexer to None, Premiere attempts to create the separate H.264 video stream as an .m4v file, but the export fails with:

Error compiling movie
Export Error
Error finishing encode
Writing with exporter: H.264
Writing file type: H264
Component: H.264 of type Exporter
Selector: 9
Error code: -1

I also tested exporting only a 5-second section, and the exact same error occurs, so this does not appear to be related to a specific frame or the length of the sequence.

The issue appears to be with the H.264 export/multiplexer functionality in Premiere Pro Beta v27.