Missing Full Sections on Nozzle Check

[casey_printer]

Both of my printheads have 1 of the 8 sections completely missing. 1 of 2 Magenta and 1 of the 8 white. The other sections look clean. I've tried system and manual head cleaning but neither worked bringing back the missing sections.

Any idea what would cause a full test section to not work? Are there any additional things I should try before replacing the printheads?

Any suggestions or information is greatly appreciated.

thank you!