iCloud not synchronising correctly with the agenda of emClient

After I launched emClient my iPhone (iOS 13) shows deleted agenda items again. (the 2 blue colored agenda parts in IOS) . Although the message 'Synchronised X minutes ago ’ is shown in emCLient, I get the agenda items back in IOS . One month ago I had no problems with synchronising. The problem started a week ago. I did not change any settings in the iCLoud settings of emClient. Can this be caused by emCLient or should it be an IOS problem (iOS is working 100 % stable although) ? I can delete items in IOS in the agenda (the blue colored agenda part in iOS), but the moment I launch emClient again, the deleted items are back.