I can't say for sure if this is a bug or not, but I will tell you briefly.

My base is built right next to the portal to the edge, where there are chests, shulkers and other blocks. I broke a few shulkers I needed and accidentally entered the portal. After I left the end portal, I found myself in the same room as I came from, but those few shulkers magically appeared in the same place. I checked it a few more times and made sure that the blocks are working and the things there are really real. The same thing will happen if I break any block, go to the edge and go back - the block will return to its place again.

P.S. I apologize in Advance for the quality