Those notes use the lower (body) octave key, not the neck key.
First check that it is actually opening when it should. If not it might just be a sticky pad (clean it with lighter fluid) or it could be incorrect springing or something else wrong wit octave mech. (maybe combined with sticky pad). probably best to get a tech to sort this.
If the key itself is opening when it should, maybe moisture is blocking up the pip (octave key tonehole). You may be able to disassemble it yourself and clean out the pip with a pipe cleaner. If you don't feel up to that, take the mech to the tech.
First check that it is actually opening when it should. If not it might just be a sticky pad (clean it with lighter fluid) or it could be incorrect springing or something else wrong wit octave mech. (maybe combined with sticky pad). probably best to get a tech to sort this.
If the key itself is opening when it should, maybe moisture is blocking up the pip (octave key tonehole). You may be able to disassemble it yourself and clean out the pip with a pipe cleaner. If you don't feel up to that, take the mech to the tech.
