Before I do the upgrade, I wanted to check if there are any known issues upgrading from Version 7.8.17 Sugar Version 6.5.25 (Build 344) to the upgrade package SuiteCRM 7.8.20 LTS using SuiteCRM-Upgrade-7.8.x-to-7.8.20.zip
I’m running on unbuntu Linux uname -a gives 4.4.0-119-generic #143-Ubuntu SMP Mon Apr 2 16:08:24 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Nothing very specific comes to mind. But your question is hard to answer, there are so many changes to the code in 3 versions. Obviously 99% of them have a positive impact, but it is always possible that a few bugs creep in.
Do you have a test environment where you try out the upgrade? The important thing is to check behaviors for the functions that are critical to you. It’s great to have a clone and experiment before changing your production system.