This is the world download with a simple contraption to quickly simulate the bug. In the dispenser to the right are the Shulker Boxes with some redstone inside.
By pressing the button boxes are placed but the comparator reads nothing until block update.
Placing the box manually instead works normally
It already has it. If you click the comparator switching it to subtract mode, the signal is not enough to pass, so you can place the shulker chest and then emit a signal through the button on the green clay, that's one of the many other types of input.
Through the button, the puls is one tick.
Through the comparator, one and a pinch