Sounds obvious but is your wheel held securely in the fork?
Pretty sure it was ok, no noticeable disc rub or wobble. Thinking about it, the steel fork has been in an accident with its previous owner, seems straight but could squiffy dropouts be the issue?
@Sion started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Sounds obvious but is your wheel held securely in the fork?