What are possible reasons for the status of a backfill to be incomplete?

Generally, this should occur during the time that the backfill is requesting runs, before all the runs are requested.

Yes I'm having that issue. I'll try to schedule a backfill for ~75 partitions and only 10 get loaded into queued runs

And this state persists for a long time? Do any of the assets targeted by the backfill have different `PartitionsDefinition`s than other ones?

No just one Partitioned Definition

This is unexpected. Is your backfill daemon still alive? You can find this out by going to the Daemons page.

It is. I'm getting this error tho. dagster.daemon.BaackfillDaemon - ERROR - Another BACKFILL daemon is still sending heartbeats. You likely have multiple daemon processes running at once, which is not supported.