Hi Rodrigo.
I don't have a lot of ideas on that issue since I haven't experienced that Fusion bug yet on my Mac.
You might try rendering the comp using Fusion's "Render Manager" window to see if that reduces the likelihood of the issue occurring. You can access this window using
File > Render Manager menu item or with the Command + M hotkey. In the Render Manager view click the "Add Comp..." button and select your Fusion comp.
If you open up the Fusion
Preferences > Memory section and lower the number of frames that are rendered at once it could help mitigate the issue. Having that value set to a high number would likely contribute to having more open files at once.
Possibly disabling the
Simultaneous Branching option in the Fusion
Preferences > Memory section might be of use, too.
Good Luck!