Thank you for your reply @runfirestop. We zipped up all files into one zip and sent a separate mp3 for the demo. So we assume that was not the issue.
But after going round in circles for a bit we think we’ve found what our problem was, hopefully;
As usual it can come down to one little letter, an A instead of a C;
We rendered from Reaper (DAW) using Target biterate (ABR) 320kbps instead of Constant biterate (CBR) 320kbps. This resulted in windows still listing the output files as 320kbps so we thought we were ok. But when we imported back into Reaper it showed the files were actually 308kbps (average). Hopefully that’s the issue that the review process had with our file.
So one useful point for other folks … just because windows says your mp3 is 320kbps, that doesn’t mean you can assume it’s the constant biterate audiojungle requires for standard quality.
Also, specifically answering the question asked in the title of this thread; windows said our wavs were 1411kbps, but as no-one on the forum has responded to this specifically we’re assuming this is normal for wavs and not an issue for audiojungle.
So unless someone needs to correct us, we can say for anyone else who has the same question;
The requirement for 320kbps only applies to mp3s but make sure it’s rendered as “constant” bitrate 320kbps not “target” bitrate or another setting, because looking at the output mp3 file properties may still say the file is 320kbps and not show you that you’ve made a mistake.
Hope that helps someone else.