A zone served by several edge pools can have a pool-specific version of some sites (the variant flag in the effective configuration), with its own origin per name. Until now, changing a proxied A, AAAA or CNAME record did not update that origin: those pools kept sending traffic to the old address.
Now an origin of a pool that was the record's old content follows the record in the same configuration version: a new content replaces it, and deleting the record, turning its proxy off, renaming it or moving the site to another zone removes it, so the pool uses the zone's records. This applies to single changes, record batches and reverts. A pool whose origin for that name is a different address on purpose (for example a load balancer) keeps it, and the simulation warns: <name>: pool <pool> keeps its own origin <address>.
The simulation's diff shows the pools that change (variants.<pool>.host_origins.<name>), so you see them before you confirm.