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This is called "polymerase slip". It happens when the growing strand temporarily dissociates from the template, then reassociates at a different spot - say, one nucleotide forward or back from where it started. If this happens often enough (as it will on polyA or polyT templates), every individual band becomes a family of closely-spaced peaks giving a 'roller coaster' look to the chromatogram.

Try sequencing in the other direction from the opposite strand, or try another primer either closer or further from the homopolymer region.