Export video with PROXY ON

We recently exporting 16 interview with timecode for my client. Each interview was filmed in 4k. 

To help my computer I alway create proxy for editing, the proxy switch is alway on! When we export the timeline normaly Premiere take the original footage for the compression. 

BUT, each time I exporting my timeline with the Proxy ON button, the audio of my exported video was in slow motion pitch. (only the audio). After a lot of change and test, I find that when I switch OFF the proxy button and exporting my timeline everything is perfect.....

Why? This bug came after the new update. Never happen before.

Footage provide from a Panasonic GH5 in .mov 100mbps 4k 8bits on a PC computer