In all 1.14 subversions, you can send items back and forth between two linked portals to maintain chunks around both portals being constantly loaded without a player around.

In 19w36a, every 15 seconds there is a chance that one (or even both) portal will be unloaded even if it received an item a second ago.

It seems like when an entity goes through a portal, it doesn't refresh portal's countdown to be unloaded.

Portal, dropper and observers are inside a single chunk on both sides. Bug confirmed by another person.