It's about conditional chain command blocks.
How to reproduce:
1. Place a repeating command block, and a conditional chain command block (set to always active) connecting to it.
2. Insert into the repeating command block:

/fill ~ ~1 ~ ~ ~2 ~ minecraft:air 0 destroy

, and set it to always active
3. Insert into the chain command block:

/say a

4. Place a block on top of the repeating command block, it gets destroyed instantly but the chain command block does not run. (Expected to see [@] a in the chatting bar)

Why I think it is a bug:
1. If the "destroy" keyword is replaced by the "replace" keyword, it works fine
2. If the /fill command is replaced by /setblock command and still use the "destroy" keyword, it works fine as well