The very same issue, today. Loose ankle, the screw spins and I open it. I think you have a broken and missing cilinder there (red arrow). I had only half of the opposite cilinder broken, so I used a larger screw, then somehow the other cilinder, the one you are missing, broke whole, so now there is no way to put the foot again. I'll try to superglue everything but I know it's not going to hold. I've just emailed dalianjj and quickly replied this: "The chinese post office can not send airmail now due to the virus problem. I have no idea when it will be available again. sorry." So I want to assume they have the spare part and sooner or later they will be able to send it.