The reason I switched the 1km & 1 Mile entries on was to prove that GC is no longer collecting new personal record data, as if it had, it would have added my latest 1km & 1 Mile records and not times that have more recently been superseded, see?
Are you using the stock Garmin apps on the watch to record the run, or other apps? I haven't had any records automatically noted since I started using "Running App Professional." I go in and manually tell it to make that particular run a record for the specific distance.
You might want to drop a note to the Running App Pro developer (https://www.rh-sports.at/running/feature-bug-request/) to see if he has any insight for why this might be happening (or not happening as the case may be). He usually gets back to me within a few days (depending on how busy he is, and how much research the answer may need). If he does provide an answer, please post here, as my curiosity is certainly piqued. I'd shoot him the question myself, but I just sent him a question/suggestion about something else, and I prefer to keep it to one thing at a time. ;-)