Did the date-field change in lay-out between your normal files and the latest one?
Are there any filters set, which make you could lose all those lines? e.g. if some values are less than or higher than...
If the load is performing as it should, then I would look first at my source data and make sure nothing has happened there.
I found coinsidently the reasen. While creating a sample file it suddenly worked. The only difference in the sample was, that I just had 1 column for a date. In my original file I had two columns next to each other with the same dates. For whatever reason QS wasn't able to load the correct dates. Each column was loaded and had dates but the wrong ones... ??
Whatever... now it works :-)
Thx for helping!