I noticed that overlapping components does not get decomposed when exporting a TTF in Glyphs. Was it always like this or did something change recently?
There is a parameter Keep Overlapping Components which should let you control this behavior. Does it not have any influence?
The problem is that it keeps overlapping components by default, which I am pretty sure it did not previously (?).
I have a look. It might have happened when I worked on the Variable font export.
Would you know in which version you changed this and when that was? I might need to re-export some fonts in worst case scenario. It would be great with an update to fix this asap, since it’s such a crucial change in workflow otherwise.
I just tried it in the latest cutting edge version and it seems to work fine. Can you send me a font that don’t work for you? And what version do you use?
I don’t use the cutting edge versions. I need to rely on a 100% functional version or I will have problems since I export fonts to clients on a daily basis. This problem is in the latest official version 2.4.4 (1075) – Please, pretty please fix asap 
Thank you!
It is fixed. You can keep the cutting edge version next to the latest stable version in your Applications folder.
In this case, this is an argument for (also) using the cutting edge version. A 2.5 stable version will still take a while. The current cutting edge version has issues with intentionally incompatible masters (masters for which you may have been using negative interpolation values) and some UI issues in High Sierra (especially displaying the Script menu). Otherwise, you should be fine.
In your case, I would consider working in 2.4.4, and opening the cutting edge version for exporting.