This is just a pure speculation, but I think we may see the teams in Jakarta for leg 3, based on a following pattern:
In season 15, teams flew to HCMC, and then take a bus to Cai Be. The next leg, they are back in HCMC.
In season 18, teams flew to Kunming and then take a train/flight to Lijiang. The next leg, they are back in Kunming.
Maybe this pattern will goes on in this season. Just a pure speculation.