ARCHICAD cannot Save a project when that project file is located inside a folder that syncs to a file hosting service (like Dropbox,Google Backup & Sync, etc.) In some very rare occasions, data loss or file corruption may occur.
NOTE: BIMcloud operation is also affected by sync utilities. It is not recommended to sync BIMcloud content with such services.
ARCHICAD’s Save function is a complicated process that involves generating temporary files, lock files and extended disk I/O operation. Most popular sync clients have no periodical check for file changes and try to sync whenever a change is detected on a monitored folder. While sync client is inpatient to send the file changes, ARCHICAD is still performing the Save operation. That results in a system lock where ARCHICAD fails to successfully complete the saving sequence of the project file.
Avoid saving ARCHICAD project files inside a folder monitored by a cloud sync utility. If you need to backup project files to such service, use third party utility that supports copying/syncing files and folders locally with scheduling features. That way you may schedule a folder synchronization job between your ARCHICAD projects folder and a backup folder inside the monitored folder of a file hosting service. There are dozens of third-party options for such tasks. As an example, .FreeFileSync Open Source application is quite popular and supports such workflows
If you insist on saving directly to a monitored folder of a file hosting service, make sure that the utility provides a function to disable real-time monitoring and use it before saving ARCHICAD files.