Colored streaks and unusual color patches on film are most commonly caused by light leaks. Light can reach the film before exposure, inside the camera, or during handling/processing.

Typical causes include:

• a faulty film cartridge letting light in
• the camera back not fully closed
• a bad seal or shutter issue in the camera
• the camera back being opened accidentally
• careless handling during processing

If the affected frames are mainly at the beginning of the roll, that strongly suggests light reached the film while loading, or the film leader was not advanced far enough before the first shot. Normally you should wind on until the film counter reaches the first exposure so those initial loading frames are discarded.

Because many frames are fine, a sporadic light leak is more likely than a uniform scanning problem. Check whether the problem appears mostly on the first few frames or throughout the roll; that can help narrow down whether it’s loading/cartridge related or a camera leak.