Inventory Collection Frequency

for the missing device you could start casper remote and tell it to run a recon for the one device now

If its an iOS device, you can' use Casper Remote (that's only for Macs) Your best bet is to continue to request manul inventory updates.
However, to shorten the inventory collection, go to Settings > Mobile Device Management Framework Settings > Inventory Frequency, and change the drop down to "Once every day" and Save. Thing is, this changes collection for ALL iOS devices, not just for one or a selection of devices, so be sure this is what you want to do. You can always set it back later by going to the same section and putting it back to "Once every week".

It only shows as 1 week being the most frequent update option we were hoping for something quicker to avoid constantly hitting the update button. Is that a JSS v9 feature?

Nope. Should be an option for you. We're on 8.71 as well, but, to be fair, we aren't using the Casper Suite for MDM, only for our Mac management. But I can go into Mobile Device Management Framework Settings and see the additional options. Hmmm, I wonder if its something that once its set you need to go to a different location in the JSS to modify it? I never recall it being that way, but, maybe check with your JAMF support rep on that. I feel you should be able to change that, so something doesn't sound right.