Please help us help you and fill where relevant:
Your LimeSurvey version: Versione 5.6.8
Own server or LimeSurvey hosting: Own server
Survey theme/template: fruity
==================
I have uploaded our custom logo and it has already happened that after a few days the file disappears and the page remains without a logo.
Does anyone have an idea why?
Thanks

What do you mean with "the logo disappears"?

So the file disappears from the folder on your server? If this is the case, I wonder if there is some kind of automatic deletion going on your server. I don't see how and why Limesurvey would delete files on your server. Or colleagues are messing with you.

It actually seems strange to me as well. I am checking with our system engineer. I wanted to verify that there was not something already known.
Thank you

Not that I am aware of. Because for this to happen from within Limesurvey, there would have to be some kind of trigger (e.g. a cronjob).

Limesurvey doesn't just start actions, it needs to be triggered to do an action. So even if Limesurvey would be able to delete this file, the deletion would need to be triggered somehow.