same here: i have a lot of gui problems with ALL of my steinberg plugins (Haloing, Retrologue, Padshop pro, AU and VST) under Yosemite with Ableton Live 9 and Studio One.
Perhaps it is a retina mac only problem???
the steinberg support says: there are no problems… very bad support!!!
I gave up reporting issues since it’s just a waste of time. I work around issues and when they really start to get in my way I use an alternative product.
Halion 5 was released 1.5 years ago and there was enough room for improvement, but above all fixing some bugs. Unfortunately there was not a single update since Halion 5 was released. I bought Halion 4 and 5 to support the development of this product, knowing it will take some time to iron out the errors and beefing up the features and hoping for some continuity from Steinberg. Unfortunately Steinberg did what they always do and left there customers in the dark with a product with great potential, but a lousy finish. 
I don’t have many complaints about HALion 5. In fact, when using it in Cubase I find H5 ‘ very useful and I can get a lot of music and sound design from it as it is.
For me, there are two issues: it’s randomly crashing Cubase when building my own presets + it’s currently useless as AU plug-in in Ableton Live.
i have found a temporarily solution for the Gui-Problems with Retina-Macs and DAWs like Ableton Live and Studio One:
You have to disable the Retina-Features for these Apps.
Open your finder, go to your apps folder, right-click on the app-icon , select “informations” and activate “Open in low resolution”.
Now my steinberg-Plugins are working (Halion 5, Retrologue, Padshop Pro)
Thanks! I thought I tested this but I might be wrong. I’ll check it out.
I ruled out this option as I was sure I had tried it. I was wrong. “Open in low resolution” solved the problem. Thank you!
It seems like this issue got worse with Studio One version 3.
Before I buy a ticket for the carousel of companies pointing at each other, I would like to know if someone can confirm this behavior or found a solution/workaround for this, since the previous trick of simply switching screensets doesn’t work anymore. I use the VST3 version of Halion 5 and don’t use S1’s High DPI Mode.
When I open Halion 5 in Studio One 3 the GUI opens like this:
When I close and re-open Halion 5, it looks like this:
When I change the Screenset to Default it will look like this:
When re-opening after choosing the Default screenset, it will look like this:
After dragging the surrounding S1 GUI frame border, it will look like this (expected result):
Fixed with Studio One 3.0.2 update!
Broken again with Studio One 3.1.0 update!
Not sure if I should report it to Steinberg or PreSonus. So I’ll put an issue report on both company forums.
Issue: The Halion 5 (VST3 x64) GUI is not rebuild properly within the VST frame after closing it.
Reproducible steps:
Result: GUI is partially build, the Instrument editor window is the size of the actual GUI
Expected result: GUI is entirely build within the Instrument editor at the right size
Result: Instument editor frame is clipped across the partially build GUI
Additional information: This issue has always been there in Studio One 2 & 3 with Halion 4 & 5. Like I said, I don’t know if it’s an issue that should be addressed to Steinberg or PreSonus. It was (maybe unintentionally) fixed with update Studio One 3.0.2. But returned again with Studio One update 3.1.0.
Video
Video of the behavior
Tested with Windows 7 x64, Studio One version 3.1.0 (default settings), Halion 5.1.1.60
Just in case someone is running into the same issue as I do. It has to do with the VST3 version of Halion 5 in combination with Studio One. The VST2 version is just fine. Unfortunately the VST2.4 version does not pick up settings created with the VST3 version in a project.
This issue with the VST3 version of Halion 5 is still standing in Studio One 3.2.
Maybe a Steinberg representative could a least chime in here and tell me where and how to get support to solve it.
Echo…Echo…Echo…cho…cho…o…o…o…o…o…o…
Ah… Stein Berg is German for heap of stones.
Stupid me, thinking it will answer back when you talk to it.
Mumbling to himself Remarkable the VST3 versions of GA4, Halion Sonic 2 and other VST3’s don’t have this issue. Maybe it’s a special feature of this State-of-the-art sampler and sound creation system tailored to the demands of professionals. Hmmmm… I wonder…
Same problem still. Damn. Great product but it seems as if it’s abandonware at this point.
727.082 minutes later…
hahahaha!
Since it seems the people developing Halion are not using electronic communication devices to communicate, these directions might help to find a solution (it will cost approximately 12 minutes to follow these).
Get in car
Take Frankenstraße to Nordkanalstraße (550 m)
Head southwest on Frankenstraße toward Hammerbrookstraße (270 m)
Turn right onto Hammerbrookstraße (250 m)
Take B75, Mühlendamm, Oberaltenallee, Hamburger Str. and Barmbeker Markt to Bramfelder Str. (5.1 km)
Turn right onto Nordkanalstraße (350 m)
Use the left 2 lanes to turn left at the 1st cross street onto Anckelmannspl./B75
Continue to follow B75 (900 m)
Continue straight onto Mühlendamm (550 m)
Continue onto Kuhmühle (230 m)
Continue onto Schürbeker Str. (290 m)
Continue onto Schürbeker Bogen (180 m)
Schürbeker Bogen turns left and becomes Lerchenfeld/B5 (38 m)
Use the right 2 lanes to turn right onto Oberaltenallee (140 m)
Continue straight to stay on Oberaltenallee (650 m)
Continue onto Hamburger Str. (600 m)
Continue straight onto Barmbeker Markt (450 m)
Continue onto Bramfelder Str. (100 m)
Keep right to continue on Bramfelder Brücke/Bramfelder Str.
Continue to follow Bramfelder Str. (650 m)
Get out of car
Walk in building
Communicate with humans in building
Awesome idea Niles, but you forgot the part about suggesting that they also hold off on using LSD during development of their software, and recommending using it for recreational purposes only. 
I’m afraid we are the only ones tripping here Orbit-50 