Can you check to see if a profile or other config went out to the Macs to point them to a non-existent SUS perhaps? If a device gets pointed to a SUS address that can't be reached, it will show 0 for the number of updates, even if there are potential updates needed.
Under Software Update Servers, nothing is listed.
I don't see any other policies or Configuration profiles that are related to software updates.
Ok, it was worth checking on though.
So, it just occurred to me that you may not have Software Update collection enabled in your Jamf Pro instance.
Go to Settings > Computer Management > Inventory Collection. See if the option labeled "Collect available software updates" is checked. See screenshot below:

It needs to be enabled in order to see any results in that Number of Available Updates field.
Wow. It helps to collect that information if you want to see it.
That was it! Thanks for your help and quick response.
I've never seen that not enabled before and thus didn't even know it was an optional thing.
That box was not checked.
Thank you!
Sure, no problem. Glad that got it resolved!
@rlowry
Be aware that checkbox ("Collect available software updates") may have been disabled by a colleague or predecessor for a good reason: It can break recon from completing.
See https://www.jamf.com/jamf-nation/discussions/25648/high-sierra-supplemental-update-breaks-recon for a full explanation.
Note that the iTunes Device Support Update in particular triggers this issue.
However, this issue was fixed by JAMF at some point. If your JAMF Pro version is ≥ 9.101.4 or > 10.2 (from memory — could be wrong) you're probably in the clear.
If you want to be 100% sure:
1. Please login to your JAMF Pro server, and view the file /Library/JSS/Tomcat/webapps/ROOT/WEB-INF/xml/JAMFSoftwareServerDatabaseSchema.xml
(modify path accordingly for Windows or Linux installations).
2. Find the available_software_updates table and verify that the version column has a size set to 255 (and not 31):
<table>
<table_name>available_software_updates</table_name>
...]
<column>
<name>version</name>
<type>varchar</type>
<size>255</size>
</column>
If the size is still 31, then you should either disable "Collect available software updates" or upgrade your JAMF Pro version.
Ok, it was worth checking on though.
So, it just occurred to me that you may not have Software Update collection enabled in your Jamf Pro instance.
Go to Settings > Computer Management > Inventory Collection. See if the option labeled "Collect available software updates" is checked. See screenshot below:

It needs to be enabled in order to see any results in that Number of Available Updates field.
Just wondering how Jamf collects the available software updates?
Is Jamf using the macos command "softwareupdate" for this?
If so, could this be a reason for a freezing of the SoftwareUpdate Daemon under macOS 12.x ?
Thanks in advance, Bjoern