I've been working on a map for a few months now and decided to export it in Composer to see how it's rendering out elements like creek labels when I noticed the exported scale was vastly different than my working scale. I checked to make sure that I'm using the same projection for both the project and composer. I decided to open it up in QGIS 2.18 and the scale looked to be the same as in the composer.
So it seems that the editing window in 3.4.3 for Mac may be off. I'm almost wondering if it has to do with the retina update for QGIS. It seems like it's basically double the scale (i.e. 1:50,000 looks like 1:100,000) Does anyone else see this issue or is there something that I'm missing?
I'm currently using QGIS 3.4.3 on OSX 10.14.2. Couple of images below to show what I'm talking about. (Top from editor window and bottom from composer export.)