Android app force to update local folder to nextcloud

Hi all,
I’m facing a annoying problem…

I setup a directory on my android smartphone to be saved on my nextcloud,
Once inset it up , it start to save files on cloud correctly but for some reason (energy saving is disabled) it stop.
The problem is that now it sync only new files and the old ones that have not been synced, remain not synched…
I choose in the setup, to work on all files also existing ones but it not worked
How I can forse the sync of a folder without adding manually files to the remote folder? Thx