Wordpress theme development -Can't see admin bar on front on my homepage

Question

i have a very weird bug on my wordpress website.
I create a theme from scratch. In my machine i use wp local. Every thing works fine.

When i publish my website, i can modify everything in all pages (with wordpress interface or FTP) except my homepage. In all other pages i can see admin bar in front except homepage. And from time to time, without any specific reason, admin bar is visible again on my homepage and i can modify in wordpress admin or ftp.
My homepage is managed by front-page.php

i believed that it was a cache problem but why only on my homepage?
I believed that was a code problem but everything works on local and from time to time it works online.

I really don't understand this bug.
Any idea please? thanks