https://www.synology.com/en-us/security/advisory
https://www.cvedetails.com/vulnerability-list/vendor_id-11138/Synology.html
You can look through all known issues.
But don't get me wrong, I'm glad they provide the information!
Don't know how much a Cloudflare tunnel protects you. Maybe it's only security by obscurity.
To answer the title, I wouldn't rely on cloud only:
https://wccftech.com/google-talks-about-missing-google-drive-files/
NOTE: This can happen with ALL providers, nothing is error free.