vSphere limits the size of the annotations to 2000 characters. Some special characters, such as new lines, get encoded as multiple characters. This can lead to exceeding the limit even though the size may appear to be within the limit.
The annotation field is truncated to less than 2000 characters so that the vSphere API will not reject it.
Take care to avoid creating large annotations that may exceed the 2000 character limit after special characters are encoded.