RubyPorto

https://imgur.com/a/dvwj4

On the barrel it's marked Z32 and the rubber has B270702 on it. (EDIT: Found another number on the front part of the barrel, in front of the metal plate, 7579334) The white markings on the barrel are 2 1 - 0 + 1 2 and there's a line on the inner part of the barrel to line the number up. The barrel extends in the plus direction and contracts in the minus direction.
The threads on the non rubber end are about the same diameter as my 67mm lens cap.

I got this lens in an ebay bundle with some unrelated (I think.) other gear (a Canon FD bellows), and have had no luck trying to figure out what it is. I think it might be some sort of view camera lens, since the metal

I'm using manual flash settings (and everything manual on the camera), and the second curtain sync works fine on 1s exposures but the doesn't fire at all on 1.3s or longer.

I can grossly underexpose the longer exposures or overexpose the shorter ones, and that doesn't affect whether the flash fires, so I don't think it's some auto-metering setting.

Does anyone have any ideas on how to get this working?

EDIT: Using the YN600 directly on the camera works on any shutter speed