Some folders can't visit and some file is missing while running

I am using the buildroot in my hardware, while it's running sometime, its file system may have chance to got problem, some folder will can't visit, such as the folder created in my project: /var/www/project/sdcard/xxx

• While the issue happen, I can't use any command(such as cd/ls/cp) for the path /var/www/project, but I can use commands for /var/www/project/sdcard
• And the xxx.db file under /var/www/project/sdcard folder will be missing, this db file keeps reading and writing while running;
• Some other files is also missing while issue happened;
• While issue happened, can't recover it by reboot system

Could you help to provide some guide about what will cause such issue, and what configuration or what log should I check while the issue happening, thank you