Missing frames occur when the triggering of the scanner’s camera is not correctly timed. Often this is a software error, but it can also result when the hardware is not carefully designed.
Can it be fixed?
No, if the frame is missing in the file, then only re-digitising that frame (or that section of the film) would allow to complete the file.
The error itself should be fixed at the scanner level (hardware and/or software).
Two errors in the same clip: missing frame followed by duplicated frame: