I've been tweaking a project for the last few days and exporting mixes, each with only minor difference from the last. But today after a few small amendments, I exported the latest mix and noticed that the Master bus meter level seemed low. Comparing the resulting waveform with yesterday's mix (using Audacity) confirmed that there was a significant difference in overall level.
So I opened an earlier version of the project and took a screenshot of console view to compare settings with the current version. The levels (volume and) of all the buses are pretty much identical. As a workaround I increased the levels by 6dB of the 3 buses that route directly to the Master bus and that has brought the overall level back to normal. But I would really prefer to know the cause of problem.
I know what some of you are thinking. Offset Mode! But no, I've checked and it's not that. Does anyone have any other suggestions about what else I could check?