My guess is that, if a drastic change in chemical or washing water temperature occurred (I'm going with the latter), then a small amount was poured in down the side of the tank, the error quickly realised, the water poured out. Assuming the film was still on the reel at that point, it would account for the odd spacing of the reticulation.

I can picture in my mind what I mean and what I think possibly happened, but I'm not sure I explained it well. I hope you can make sense of that garbled idea!