I am experiencing this again in 1.14.4!
Insta-breaking blocks (in my case, netherrack) while the player is falling (in my case, making a downwards staircase) creates client-side ghost blocks. I am on a Realms server, and I am using the pre-release of Optifine. More testing may be required.
I've seen something similar three times now on Java Edition 1.14.4. These three instances occurred on a multiplayer survival world around pillager outposts. The one I witnessed ended up with around 100 pillagers in the same area around an outpost (not all pillagers are in the screenshot below).
[media]A second documented instance:
[media]