Colored blocks or checker patterns that appear for one or multiple fields/frames in the video and are commonly associated with (but not limited to) issues during tape capture or file transfer.
If your source was a tape such as DigiBeta, HDCAMSR etc then it is likely the issue was introduced during tape capture. This could be due to either tape damage at that point or dust/debris being present on the tape or within the tape deck itself. In this scenario the issue may appear slightly differently each time the tape is checked at that point, and on occasion may even be concealed entirely. Verify the tape is free of damage, dust and debris and the tape deck heads are clean. Re-capture.
If the issue is printed on the tape the issue was likely introduced during tape dubbing. Seek an alternate tape source free of the printed error.
Occasionally the issue will be data corruption. If this source file had previously hit the automated QC error code ANALYZER-VideoDecodeErrors or ANALYZER-VideoDecodeErrorsSecondary it is possible we reviewed the error, could see no issues manifest and overrode the error. However the issue then manifested itself during the encoding of the Netflix streams. If this is the case then an alternate source free from the issue will be required.