Good morning folks! Indeed, as some of you suspected, it appears to be right handlebar control. Disconnected it and the left turn signal stays on (latching).  I disassembled the right hand control and tried to clean contacts as best as I could with electronic part cleaner spray and 1200 grit paper, but still the same. In fact, while kill switch works, starter button doesn’t work (no crank). But I am getting crank when jumping its leads (solid green and black/green, I think). So I created external loop with push button switch I found in my garage and it works for starting engine. So I am thinking to add similar external loop to bypass cancellation paddle, just not sure how to do it.

not all fuses are quality.

Get the brand LittleFuse ATOF with TIN coatings NOT the silver version. ATOF is the current version of ATC fuses. Yes, replace them all. Doing that as well for my k and Brutale. I've just gone down this rabbit hole. Grainger is the supplier with fresh stock arriving after the new years. Look on LittleFuse website for distribution. Buy backups.

Okay. Would you define "reba." Also, that relay unit doesn't have "warnie" printed on it; it has Warnbl. Warnbl. is the German abbreviation for warnblinkanlage meaning "hazard lights" which can mean turn signals and/or emergency flashing lights.

I believe your problem is within the right switch gear, as Ingo indicated. You probably need to disassemble that to a degree in which you are comfortable and study the action of the turn signal cancellation button. Here is a tutorial covering disassembly of the right side switch gear. It is a European switch gear that includes the headlight switch but the Cancel function of it is the same as on our US switch. You should obtain DeoxIT D5—a superior electronics cleaner—and clean all connections of that switch. I had problems with my headlight switch not lighting the high beam; DeoxIt restored its function.

Disassemble the switch within a large box so spring-loaded parts and other small part don't get away from you. Click the link below the line to view the PDF.

Are you sure the cancel button is not shorted/grounded?

This is the actual reba. I haven’t modified it in any way.