Brother GTX-4 Instruction Manual page 199

(6) Check to see if the printed result of both sides are acceptable, and if no ink-jet droplets have been ejected, perform
a head cleaning for print heads.
<IMPORTANT>

If the print result shows an intermittent line, non-ejection has occurred. A head cleaning should be performed on the print
head that has a poor nozzle check result.

Even if the lines of the white-side printed result are light, since white ink is fired from more than one nozzle on the same
place, the quality is not affected.
<TIPS>

For details, refer to "7-2-2. Head cleaning >>P.200".
Non-ejection occurred at the arrowed area.
Example:
Precautions to keep good printing quality/use printer over the long term
On the color side
Non-ejection occurred at the arrowed area.
Example:
199
On the white side
X0141