When the SD-FEC IP has been configured using a Windows OS with the Parameter_Interface parameter set to "Initialized" or "Initialized retain I/F", so that the IP will automatically configure the code parameters, the IP behavior will be incorrect.
This is due to an error in the memory initialization file (MIF file) generated by the IP which is used to configure the code parameters.
The ECC bits defined in the MIF file are incorrect and result in the IP corrupting the code parameters.
Due to the nature of the error, the IP behavior will vary depending on the conditions of use.
This is a known issue for the SDFEC IP in Vivado 2018.1 and 2018.2 when it is generated on Windows OS.
You can use a Linux OS to work around the problem.
Alternatively, use the Run-time Configured setting for the Parameter_Interface and initialize the code parameter via a processor or a programmable logic based controller using the command transaction log generated by the IP.
See the "LDPC Runtime Configuration" section of (PG256) for details.
For Windows OS only users :
For other known issues of Soft-Decision FEC (SDFEC) Integrated Block, see (Xilinx Answer 70720)