You called uint32 CySysSFlashWriteUserRow(uint32 rowNum, const uint8 rowData) API to write the SFLASH row, right? If this API returns success, there has no reason the SFLASH ROW is still empty. Are you sure you read from the correct address?
If you have a Miniprog3, i recommend you run the "PSoC4-BLE-SFLASH-Update.exe" tool locate in path C:\Program Files (x86)\Cypress\Programmer\Examples\Misc\PSoC4-BLE-SFLASH-Update\Executable, write some bytes into SFLASH of PSOC4100S(this tool can be used for PSOC 4000S/4100S SFLASH update also), then read the SFLASH content out use your own code, if the result still empty, maybe you don't read from correct address i think.
thanks for the answer, I'll check that out.
I updated the file WriteUserSFlash.c with the one from the example (not the one from my other project).
Difference: number of bytes written (changed from 0xFF to 0x7F ... of course, 128 Bytes Row Size)
checked addresses (seemed to be ok)
Watched memory blocks in debugger and the rows were updated.
So, seems to work, thanks you for your help.