For a few weeks now my line isolate works fine but when I open the drawing again, I have to run line isolate again. For some unknown reason the isolation is not holding and all the lines are refreshed when I open the drawing again. I am using Cadworx Plant Pro 2010 and I never have run into this issue before. If any users in this forum has a fix, I would really appreciate it. Thank you.

What is the build you are using?
I am using the
CADWorx Plant Professional 2010 (Build Date: November 10, 2010) (32 bit)
and can not replicate your issue.
If I isolate and close the dwg. and then re-open the lines remain isolated.

Are the isolated lines on an external reference? CADWorx displays all of the lines when loading or reloading an external reference.

Not sure if I understand what your problem is exactly, but you can try this;

VISRETAIN set it to 1

Let me know if that helped.