You mentioned that you clean out your machine as per the manual instructs.
However, does the manual suggest using canned air?
I don't have yours, but do have a Bernina 820.
My service tech was very firm to never use canned air, as it will just blow the lint around ... and potentially send it further into the machine than can be reached. Meaning the need to send to him for servicing sooner!
Instead, the bobbin area should be brushed or vacuumed out regularly.