Update 1: The bug is fixed in .NET 4.7.1 (thanks to Pascal van der Horst for the information)
Update 2: The related bug is fixed in CMS Core 10.10.2 and 9.12.5. If upgrading to that version is not an option, you can contact Episerver support service for further assistance.
If you are using Episerver and update to .NET 4.7 (even involuntarily, such as you are using DXC/Azure to host your websites. Microsoft updated Azure to .NET 4.7 on June 26th) , you might notice some weird performance issues. If your servers are in Europe, Asia or Australia, then you can see a peak in memory usage. If your servers in North America, then you can see the number of database calls increased. In both cases, your website performance is affected, the former can cause your websites to constantly restarts as memory usage reaches a threshold limit, and even more obvious in the latter. Why?
It was a known issue in .NET 4.7, as mentioned here: https://support.microsoft.com/en-us/help/4035412/fix-expiration-time-issue-when-you-insert-items-by-using-the-cache-ins