How to reproduce: Break the block underneath a gravel block and place a lantern/hanging sign/dripstone/button below the gravel on the same tick.
Observed result: The gravel and lantern/hanging sign/dripstone/button floats in the air
Expected result: The gravel and lantern/hanging sign/dripstone/button will fall/break (actually, falling gravel is an entity, so you should not even be able to place blocks below/on falling gravel at the first place).
Reason: Gravel is supposed to fall and lantern/hanging sign/dripstone/button breaks when without a top support block.
Unless I’m reading or replicating your report incorrectly, this doesn’t describe a bug, as any falling block takes one tick to update to an entity. It is impossible for this to occur on the same tick like you described by design.
Try running
/tick freezeand setting up this structure, you will find that if done within the same tick, neither the gravel will fall nor the lantern break.