Check this video for an example of the bug: https://youtu.be/hGhqyq2NGeA

I couldn't reliably reproduce the bug in singleplayer, but it was reliable on a multiplayer server with 40ms ping. Steps to reproduce in creative mode/opped, using Fancy graphics settings:

1. Start a new server, probably a non-local one so that there is ping.
2. Run the command in creative mode: /give @s repeating_command_block
3. Place down the block, right click to configure the commandblock.
4. Set Always Active to true, set the command to anything non-empty. I used effect clear @p.
5. Break the command block, it should flicker briefly before being destroyed.