Is This an Adobe Acrobat Message or has Malware Infected This Computer?

Hi, I'm the IT guy for a small business. We have about 25 computers with the Creative Cloud, and 10 computers with stand-alone (one time purchase) of Adobe Acrobat.

Recently, one of our computers showed this error/pop-up. Not sure if it's malware or if Adobe has messed up the serial number for our user...?

"A recent scan of your Adobe software has determined it is non-genuine. We're here to help fix it..."

This user has had this exact computer for 3 years. The serial for Acrobat was purchased online from a reputable, authorized reseller. I purchased this myself, so I know there's been no 'funny business' with the license or the computer.

Since I know for a fact this is a legitimate copy of Acrobat, my first reaction was that this computer was infected. I ran several scans but found nothing. I didn't even consider it was a legit message from Adobe, because we don't use pirated software. Wasn't even in the realm of possibility.

I found this thread which mentions using the cleanup tool, but it seems it's only for the creative cloud...? (The copy of Acrobat in question is stand-alone)

Any ideas and suggestions are helpful. After 3 years for this computer, and probably 2 decades of being an Adobe customer, getting the pop-up message every time the user opens Acrobat is not good.