The bug

Upgrading from 1.12.2 to newer versions will cause trapped chests placed in 1.12.2 to stop triggering redstone through the floor.

How to reproduce

1. Open a world in 1.12.2 and place a trapped chest with some redstone dust under the block the trapped chest is resting on, have some redstone output to test that it's working properly, and test it. It works fine.
2. Close the game and open the same world in the current version, doing the same thing with a new trapped chest.
3. Test each one. You'll find that the one you placed in 1.12.2 no longer triggers redstone through the floor, only from the sides. The one you just placed in the newest version works fine, giving you two identical trapped chests with different behaviors.