From my experience it's not all that unusual, though to say exactly what causes it - I can't. I surmise that it could be some dried material shifting about on the print head through the cleaning process itself, which may perhaps indicate an issue with the wiper blade, but I put heavy emphasis on the word "surmise". One thing you should NOT do however is run successive cleaning cycles without making a real print in between each one. This is because some of those gaps may not be clogging material moving about, but air spaces that develop as a result of the cleaning process. Epson technicians have advised me to print between each cleaning, and ever since then I have found this advice to be very useful. Once you have completed three or four cycles of clean-print-clean-print and you are still getting gaps on the check sheet, make another print and trigger a power cleaning. With all that, you should be restored to normal, unless there are deeper problems.
