Deleted values on timesheet

Hi,

A lot of people use Projeqtor but i have a specific issue for one team composed of 3 ressources.
They completes their work every day, for each assigned task.

Sometines, on their timesheet, some values of a ressource on a task disapear, like there never been some allocation done by the ressource. I found a 0. Sure 100% that allocation have been done by ressources. Not always the same ressource, not always on a specific day or the same activity. It's weird.

Do you know if this is a bug or if there is an option somewhere to disable.