mystery ti frame fabricated by Sandvik?
To my eyes your frame seems to share a lot of design features with Sandvik produced frames (say from around the late 1990s?).
For example, the way the headtube has been machined is strikingly similar to my Bonty ti-lite, as are the drop-outs , cable routing, and tube profiles -no gusstets though! Whilst the rear triangle looks very much like my old (non-disc) Cove Hummer. Both of these frames were made by Sandvik (who make loads of frame for loads of people), so exact 'brand' still remains a mystery though...