I just noticed this after upgrading to Fedora 28, and if you’re experiencing the same thing I am, then I think it’s part of updates to the GNOME shell.
Open “GNOME Tweaks” (or install it if you don’t have it already), then select “Keyboard and Mouse”.
At the bottom, there is a section for “Mouse Click Emulation” - my default changed to “Fingers”, meaning a two-finger click is a right-click, and a single-finger click is a left-click, regardless of where the fingers are on the touchpad.
You can change it from “Fingers” to “Area”, which should restore right-clicking via the right side of the trackpad.
Hope this helps!