Errors follow changes.
THE QUESTION
What was different immediately before this started?
Almost every new error has an answer.
COMMON ANSWERS
A plugin or theme was updated A new plugin was installed The PHP version was changed A file was edited A migration happened A setting was changed A developer worked on the site Traffic increased
IF YOU DO NOT KNOW
Check what was recently modified. In File Manager, sort by last modified date.
Check the application's update history.
Check cPanel > Metrics > Errors for when entries began.
Check your own email for update notifications.
IF NOTHING CHANGED AT YOUR END
Something changed elsewhere: an external service, a third-party script, a certificate expiry, or a domain renewal.
Certificate expiry and domain expiry both produce sudden failures with no action from you.
THE HABIT WORTH BUILDING
Note what you change and when. A one-line record makes future diagnosis considerably faster.