While performing some tests before upgrading our server to 1.14 we encountered a problem with droppers.

What has happened?

In the Pictures you can see a simple dropper elevator. The dropper on fourth position from the bottom gets stuck in "triggered:true" state if the elevator is used. After that the dropper remains in that state, regardless of the surrounding redstone signals.

So this behavior is blocking the function of the item elevator.

This does not effect all droppers, but a few random ones... it does not help to replace them as they stay affected when triggered once. We discovered a few more of them in our contraptions just in case you need more examples.

What should happen?

The item elevator should transport the items from the bottom to the top.

This was working in Minecraft 1.12.2, and some quick tests in 1.13.2 were successful, too.

Bypass the issue?

We discovered that this could be bypassed when the slab next to the affected dropper is replaced by a solid block (and adding another way for the signal).

So this issue may be connected to dropper, coordinates and slabs, but we haven't investigated furthermore...