I have a BenQ EX3501R monitor connected by HDMI to my MacBook Pro, which is a Early 2015 model.
The issue being that OS X gets the resolutions completely wrong - the monitors native resolution is 3440x1440 but it switches it to 6720x3780!
Alt-clicking the 'Scaled' radio box does not list the correct resolution.
For further confusion, a Mid 2012 15' MacBook Pro connecting to the same monitor via the same HDMI cable works fine. The only notable difference is that one has a GeForce chip, where as mine is Intel Iris.
Both are running latest Mojave 10.14.1
any ideas of a way to proceed?