I am going to pull you into private, and see if resetting the voicemail will help.
After several calls to care, chatting in and finally a trip to the store, no help. However in piddling around in the app, I seemingly resolved my issue with the S8+. Voicemail app>settings >preferences>mobile ad preferences. I just accessed the preferences, I didn't change anything. It spun for a few seconds and as it did, the missing messages began to appear 1 by 1. I backed out of the settings and all seems to be back to normal.
I am glad it helped. It was just a random fix from me messing around with it and that was what worked. Congrats!
Thanks for stopping by to help share what has worked for you! That's very helpful for others who will be visiting and looking for assistance.
There are also a lot of instances where we can access a customers account, remove/re-add their voicemail services, and send some refreshers to their device to get them back up and running.
Hopefully these posts find the future users needing help!