Yes — those symptoms are consistent with a sticking second shutter curtain. A shutter that doesn’t close on time can leave the whole frame overexposed, or create a bright strip along one edge if it begins closing late and then frees up partway through the exposure. The fact that the band rotates with camera orientation supports this being a shutter issue rather than a metering or scene problem.

The burst sequence also fits: first frame badly affected, next frame partially affected, then later frames normal as the curtain works itself loose.

This is generally a mechanical fault, not a flash-sync setting problem. There usually isn’t a reliable user fix beyond basic checks like making sure no flash-related settings are active and confirming the issue persists across modes. If it keeps happening, the practical remedy is shutter service or replacement — and on an older body, replacement of the camera may be more realistic than repair.