If the pixel dimensions are reduced when you export, then it is either-
1. You have the option to 'Resize' checked 'on' in the Export dialog, (and some dimension info, like 1600 long edge), or
2. You have done a crop, which will reduce the pixel size dimensions (unless you do an enlarge re-size in Export)
Note: we are talking pixel dimensions here- nothing to do with file size. You mention 30Mb files, but this has no relevance to exported images (unless you export the 'original' )
sorry for being incorrect: I meant 30 megapixel when I referred to my camera.
I did neither check the resize button nor did I do the crop on the images in question. That is why I'm so perplexed.
Any other ideas?
I just found the solution: I have lost my server connection so the export function used the preview files instead of the original files. What a bummer! I spent so many hours yesterday night. Why did Lightroom not warn me?
Thanks for posting your own correct answer.
I have learnt something also from your experience. And perhaps another reason why it is not recommended to store originals on a NAS.
I agree- "Why did Lightroom not warn me?". I experience the same on my 'home' system. Seems it allows us to export images smaller than we might want. (my export test without resize was 2560 long edge from a smart preview image of 6016 long edge original)
Perhaps log a suggestion for an Adobe fix in the export module over at- Photoshop Family Customer Community