Pathfinder yielding unexpected result

[BSaxman]

Trying to make several logo files transparent. I've always been able to use the pathfinder tool to divide or trim and then delete the areas I want to be transparent. I'm getting an unpredictable result, in more that one file. See the attached photo for further explanation. Black fill is NOT set to overprint. Any ideas?.

[Ray Yorkshire · Accepted solution]

Does it go away after View > Preview on CPU?

It could be your graphics card not getting on with the GPU

If so you could update drivers , or relieve work load /  do housekeeping on computer

[BSaxman]

Doesn't go away on screen, but prints OK. After some housekeeping I'm back to my normal workflow. Thanks for re-directing my efforts!