I still aim to fly this deal and contacted both priceline and LATAM on twitter (yeah I know but I can afford spending hours on the phone today) to get clarification on why the IB MAD-GRU segment was removed from the booking of my girlfriend (in addition with the LA operated GRU-SCL which was removed - just like on my booking, but that we can live with). LATAM was the first to reply indicating as expected that I should check with the OTA and said that LATAM did not cancel any flights and that "two flights are operated by IB"...
Priceline replied that I should reach them by phone and that he added a note on file regarding my request...