has this only happend for a single account, or for all accounts all over the system?
Have you recently changed anything to the vaultwarden docker-container?
How did you login to vaultwarden? Via an application (Desktop, Smartphone or Browser extension)? If yes, try to login using the webvault.
I once had a similiar problem, when the bitwarden application got updated and i couldn´t see my content afterwards. Accessing the vault via a webbrowser showed all its contents.
Check your Vaultwarden logs and/or reverse proxy logs. Maybe your reverse proxy is configured to limit response sizes or something, and your vault has now gone above that limit.