After developing a negative Ilford HP5+ I got a white stripe on one side of the negative. The strip is irregular in shape and it's about 0.5-0.8cm width.
Today I double checked tank, reels to be sure that all is clean. Also mixed fresh chemistry and processed another 120 roll of HP5+.... got the same stripe. It has happen to me 4 or 5 time during last 5 years...I have no idea what can cause the problem.
Any help would be appreciated.

Thanks you

PS. image attached (fragment of negative, half of the frame)