For mixed mode transaction, we may see eviction concurrently removing records from the history store while we are still checkpointing the history store.
Here's one scenario.
Checkpoint runs on the page.
We commit a mixed mode delete with timestamp 0.
We commit another update on the key with a normal timestamp.
Eviction runs on the page writing the new update to the disk and the 0 timestamp tombstone to the history store.
The 0 timestamp tombstone causes all the history store content of that key being removed.
Checkpoint runs on the history store.