When I correct the number of lengths I swam in a pool swim activity, the average pace for the entire swim changes to 0:00 on my phone, and on the web shows --. This is a recent change, as in the past on my phone it would recalculate to the new, correct overall activity pace.
Giving this a bump for some attention
I just tested editing a swim in Garmin Connect Web, changing the number of lengths, and the average was adjusted correctly.
Here's from a swim I just did a lunch. Before and after editing to add 5 lengths my watch missed:
