Welcome to the complicated and frustrating world of macro stacking
I do agree something appears to be off with your stack as I can clearly see some halo effect going on as well as overexposure; a few things might help/be responcible:
1) Overexposure - you have to be really carefull with stacking as it can blow out composit images where the separate images are infact not overexposed, but very close to it. Also you have to avoid clipping in the colour channels and I suspect this is what has happened here. If you can view a histogram of the image and have it show each colour channel (red, blue and green) I suspect you will see a few hotspots (on teh rear bud) as well as quite a bit of the red channel clipping the right hand side of the graph. If you tone this back in editing the image (remember if you adjust the whitebalance do the same for all 3 images - infact try to keep all editing before you merge the same).
2) Blur and the odd halo - afew things here:
2a) image order and focus. Double check that the series of images you captured cover the whole desired focus of the image and that between each shot there is some overlap to the previous shot (the more overlap the better).
2b) when you import the images into combineZM make sure that you import them in order - front to back or back to front - but they have to go in order. If one image is not in order the merging software will get confused.
for refrence with the program this is my general order of use :
Open Combine ZP
From the little bubble window that appears select the "Enable menu" control (second icon on the right)
Go to "File" then "New" and select the desired images in order (remember order must be kept)
Once the images are imported go to "Macro" then "Align and balance used frames (thorough)"
Then once that process is complete "macro" then "Do stack"
If the stack fails to work you can try experimenting with do "All methods" which will create and save a folder in the source of where you got the images for the stack from containing stacking results from all the stack process it has. This might take some time.