I can't say for sure without examining the images, but it looks like when the background was removed, it was not removed cleanly, so when the images are stacked on top of one another bits of the background are emphasized. it also looks like the background on the image you posted may have had some magenta in it because there is a color build-up along the edge of the hair.
To check the image, you could Ctrl click (Windows) or Command click (Mac) on the original layer thumbnail. That will load a selection of the pixels on that layer. Then choose Select > Select and Mask. In the Select and Mask Properties panel, choose Black & White. That should pretty clearly show iif there are any white or gray areas in the background.
How to fix the background and make it cleaner is a whole other question.
Thanks Barbara - Yes I tried this already and the image is perfectly clean. There are no stray elements at all anywhere on the image.
Apparently you do not quite understand the effect of superimposing Layers/pixels that have low opaqueness. (edited)
As a work-around you could, Instead of adding multiple Layers with transparency, create a Group with the transparency as a Layer Mask and populate it with the layer copies without transparency.
To remove the transparency from the Layer use Layer > Layer Mask > From Transparency and then drag the Layer Mask over to the Group.