Collision Detection error 'Changes cannot be saved' when a record is edited

When editing a record*—via either a full edit or an inline edit for standard objects that use Aura record home—that another user, the same user in a different window (Lightning Experience only), or a background process has changed, users see this message:

Salesforce Classic:

"Changes Cannot Be Saved. The record you were editing was modified by User during your edit session."

Lightning Experience:

"This record was modified by (User) during your edit session. Make a note of the data you entered, then reload the record and enter your updates again."​

*Note that when making an inline edit for all custom objects and standard objects that use LWC record home, the record page automatically refreshes unless another user, the same user in another window, or a background process edits the same field to a different value. In this case, in lieu of the message above, users see a message showing them the conflicting field values. Users can choose the values to keep and save the record.