'every' interval seemingly not respecting 'first_at' for non-persistent schedule

[twilbrand]

I have a non-persistent schedule with a job that has the following in it's configuration (there is not a cron config key):

...
every: ['1d', {first_at: Chronic.parse('04:31')}]`
...

Chronic.parse outputs: 2020-12-12 04:31:00 +0000

I would expect this to schedule the job for 4:31 UTC upon startup and then run every day at 4:31 UTC. However, the job is getting continually queued and run at 21:51:48 UTC. In fact, every job that has an interval of 1d with different first_at values is getting run at that same 21:51:48 UTC.

What am I missing?

Resque: 1.27.4
resque-scheduler: 4.4.0
rufus-scheduler: 3.6.0