First of all, please make sure you have the latest version of the app.
Then check if there are any files download errors in Settings, and try starting download:
1. Go to project list;
2. Open side-menu;
3. Go to settings (press gear icon);
4. In settings, view go to the "Other" tab;
5. You will see the section "Files on device";
6. Check if you see any errors in this section;
7. Press start download.
If that did not help, the issue might be caused by external apps on your device, such as antivirus software or auto-clearing cache apps. If you have any of those, try turning them off to see if that helps.
If those steps won't work, please take a screenshot of the error in Settings and contact our Support team from the app.