I see Fireware 12.6.x is using kernel version 4.14 vs. 12.5.x using 3.12.
Is this way we see so many issues with both fireware and management software?
There are some issues related to the kernel change, but for the most part are performance related -- you can view current known issues under the Known Issues (or KI) portion of the knowledge base.
Is there any specific issue that you're running into that I can help with?
WatchGuard Customer Support