This repository illustrates a bug in Safari on iOS 17.5.1 where setting object-fit: cover style on a video element is not applied, depending on the value of some padding on the enclosing element.
For instance, if the padding on the element is set to 15px, the object-fit: cover is not applied. Resetting the object-fit: cover on the element, after briefly setting it to some other value (like contain), resolves the state.
Apparently the behavior is in some way related to value of the padding. Setting it to some slightly different value like 16px also does not trigger the issue.