SPSS wont analyze all cases in sample despite no filter being applied


I have a large number of cases (about 3000) in my data set as well as a bunch of variables. Now when I run analyses (e.g. descriptive stats) I always get results for only approx. 2500 of them (the results also always yield 2500 valid cases and 0 invalid cases). Even when I run a frequency table for the running ID (1 through 3000), it only results in 2500 valid cases. For the IDs 1300-2000 it shows 0 as a count which simply cannot be true (I cheked using data view and there are entries for the ID as well as for all variables). Also, the number of 0-counts for IDs is approx. 700 so does not match the difference of 500 that I get.
I have checked numerous times and there is no filter applied (such as select cases if etc.). Any suggestions what the issue may be? These are greatly appreciated!

Thanks in advance!