I am noticing this A LOT when a tornado hits. It leaves red outlines of blocks that it is either trying to remove and not removing or that aren't being loaded. This is in 1.12.2. I have gradual block repair active in the config, (don't know if that is causing it or not).

So those are repair blocks and its a placeholder for the grabbed blocks to repair over time since this is still WIP.

K. I wondered as such. Didn't know it was still a WIP. I wonder if there is a way to make those transparent for public release versions.