Black point when take picture

Hi all,

My Panasonic Lumix is an excellent material for what i do. no need of extra things. It suits me perfectly.

But, actually it give me some bad results.

For any know reason, some picture i take have a black point on it. the black point seems to appear in some particular situation, like a little zoom or with a more longuer autofocus time.

This give to me some pictures with a black point.

Do you know from which part of the material could be in cause ?

Is it Lens ?

Thanks in advance for any answer you can give me to help.

Best Regards.