Hi Genmare,
I've only tested one of these files in your folder.
It struggled a bit right before the end but then finished and was playable.
In general, if you experience the same issues via browser, it is definitely not a JDownloader issue
If you experience more issues downloading these files IO would think about purchasing premium and then try it via official download(-button).
If you want to use JDownloader to download via chomikuj.pl (premium) account you can add your account via Settings --> Account Manager.
Also make sure to disable the stream download, see:
Settings --> Plugins --> Chomikuj.pl
-psp-
EDIT
I've tested all objects - they did disconnect multiple times during the download but it successfully resumed until finish!