If the film is not loaded correctly you would experience an out of focus or soft edge. It may be the film transport mechanisms.
Has this fault been recent? When you mention about using shorter rolls, are you experiencing the overlapping near the end of the roll?
Here is a link about common issues with a widelux F7 (I think all models have similar mechanics). There is a similar issue as yours, related to damaged teeth in one of the film transport gears.