Why is logic inserted into my clock domain crossing path?

Due to a problem in the Intel® Quartus® Prime Pro Edition Software version 19.1 and later, you may see logic will placed in the clock domain crossing (CDC) path. The source of CDC path should not be touched during retiming but this requirement is not being honored.

A patch is available to work around this problem for the Intel® Quartus® Prime Pro Edition Software version 19.1.  Download and install Patch 0.59pro from the appropriate link below.

• Download patch Intel® Quartus® Prime Pro Edition 19.1 Patch 0.59pro for Windows (.exe)
• Download patch Intel® Quartus® Prime Pro Edition 19.1 Patch 0.59pro for Linux (.run) 
• Download the Readme for Intel® Quartus® Prime Pro Edition 19.1 Patch 0.59pro (.txt)

This problem is fixed starting with the Intel® Quartus® Prime Pro Edition Software version 21.3.