Thanks for the info. I am the original owner for the one that is running at 97-98 since 2018 and I only recently observed the CPU turn down due to high temp. Otherwise it has been very stable. I got the second one from ebay last year (also 2018 model) as well but running at 86.The one at 86C is about right, the one at 97C perhaps has failed or incorrectly installed thermal transfer pads. You can fix the CPU temperature easily, but the router has more issues. Read what I found inside. I had a full bin of dead AC86U's, kept 10 for experiments, repaired 3 using the others for parts, kept 1 in my routers collection. My recommendation is to replace them with something else when you have a chance.
A few days ago I got a refurb model from Amazon that was made in 2020 and running mid 60's. So looks like they used slightly different thermal solution now.
Let's see if I can salvage the one that is running hot and extend its life for a few more years. I will let you know how much the temperature drops after the thermal pad replacement.