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I can prove this by poking it with my needle,see a hole, but scar tissue won't develop.
Is it cause by sunburn or fungus?

Hello Kris,
your Harrisia jusbertii does have a fungus growing on those lesions. Image two from the top does show a lot of black specks on the sunken, large lesion. Those are fungal fruit bodies, which contain fungal spores. Now the question is: Are we looking at a secondary fungus, or is the pathogen responsible for the formation of these lesions? A secondary fungus develops on dead plant tissue, but was not the cause of the lesion, i.e. it is generally a saprophyte. The last image does show rotting pulp underneath the epidermis, while image five shows healthy looking plant tissue.
Are the lesions concentrated on one side or are they equally distributed around the stem? Sunburn damage will most likely be visible at the tender top (crown) and the ribs on one side.
You can go ahead and do a little surgery. I would at the very least take that lesion with the fruit bodies off. In case this is a primary pathogen, it will release many spores and cause numerous additional lesions on your plant, if it is allowed to remain in place. Then I would watch the plant closely for additional lesions or enlargement of the lesions already present. That again would point to a pathogen causing the problem.
If you do have a healthy portion of your H. jusbertii, you can also separate it from the affected part and try to root it. That way you will not lose your cactus altogether to a disease.

Harald