Here is another picture, really bad trunk.

Any pictures of the rest of the plant? Are the leaves healthy?

Hello,

Yes the Plants are healthy except the Trunks are cracking ...Should I cover the Trunk with something? thank you by the way...Here are the Flowers of the Plumeria...Called Pink/Orange Rainbow

Here is another pics that show the Leaves are healthy...

COULD be residual effects of previous sunburn damage, BUT, I don't know the strength of your sun or temps. Are the damaged areas all facing the same direction (provided you have not moved the plants)?

I agree about the old sunburn.

There are also some plumeria that have naturally very gnarly bark, or bark that tends to split and get ugly at wound sites. It doesn't seem to be affecting the plant, though, so I wouldn't worry about it.

Thank you all...The Tree it's planted on the Ground, it's possible that is causing too much Sun, but it's healthy...Now I feel god knowing that this is not something I should worry about...Nice to know.....Thank you all once again, greatly appreciate it!!!

I agree. I wouldn't really worry about it they're very hardy plants. I have a plant thats trunk is ripped in half and it still fine. it's flowering at the moment. Yours just really looks like sunburn. When they are sunburnt the trunk tends to split and turn into a brown color.

Thanks for posting your Plumeria Pics at least now I have a comparison to what others Trunk look like...Greatly appreciate it....