The issue is most likely caused by a mismatch between the date format in the PayPal statement and the date formats supported by Flexi:
CZ date format [31. 12. 2018]
US date format [12/31/2018]
UK date format [31/12/2018]
There is an additional US format: 2018/12/30. For these cases, it is necessary to configure advanced parameterization linked to the CZ format. parametrPaypal.xml
This parameter overrides the CZ format with the yyyy/MM/dd format. After uploading the parameter, Flexi must be restarted.