Things to check

Trailing colon

Source and translation do not both end with a colon

Glossary

Source Translation
No related strings found in the glossary.

Source information

Source string location
imageplugins/channelmixer/channelmixer.cpp:187 imageplugins/channelmixer/channelmixertool.cpp:177
Source string age
a year ago
Translation file
po/cy/digikam.po, string 626