You can access the logs directly from the Drive Client DB files.
To do so, first install sqlite3 in your Windows machine:
winget install SQLite.SQLite
Then, run the following command:
Bash CLI:
sqlite3 -csv -header /c/Users/USERNAME/AppData/Local/SynologyDrive/data/db/history.sqlite "SELECT datetime(update_time, 'unixepoch', 'localtime'), path, not_synced_reason FROM history_table WHERE is_not_synced=1" > /c/Users/USERNAME/Downloads/unsynced_logs.csv
PowerShell:
sqlite3 -csv -header C:\Users\USERNAME\AppData\Local\SynologyDrive\data\db\history.sqlite "SELECT datetime(update_time, 'unixepoch', 'localtime'), path, not_synced_reason FROM history_table WHERE is_not_synced=1" > C:\Users\USERNAME\Downloads\unsynced_logs.csv