Its the entire platform, not a single modpack. You keep pushing things out as "stable" when they are nowhere close to it. You never give server admins any warning and it causes havoc for anyone running a custom mod pack. Not to mention that the built in modpacks are broken as well. For example this shot.
In the background you can see crash files from a custom mod pack that's broken, but this is about the Tekkit modpack that is part of the platform. When you launch it, it asks you if you want to update. I clicked yes, it downloads the files and when its loading you get this. Obviously this wasn't tested at all if there are incompatible versions built in.
On the custom mod pack side, every time you guys change something the custom mod packs are broken. Last time around the launcher wouldn't even pick up the custom mod packs, wouldn't save settings like RAM allocation, and you moved the location of saved games without notifying anybody. After everyone got their saved game locations moved, you updated the launcher and fixed the mod pack loading and settings were being saved, but you moved the saved games back to their original location and caused another round of breakage. Again without any notification. Nothing in the change logs.
You have a setting in the launcher for using beta builds. Why don't you actually use that to its full potential? Setup a forum for beta testers to report problems, and a separate forum for server admins to report problems that arise in custom mod packs due to launcher changes. If you had the infrastructure in place on the forums, I have no doubt that lots of people would give you input BEFORE you mark something as stable and push it and cause all kinds of problems. I know I would. I would have no problems at all adding a test world to my current server configurations and having 10-20 people run through it so problems could found before they became mainstream.
As things are now, I am tired of getting screamed at once a month because of problems caused by the platform when I had no idea changes were coming. I understand that you cannot possibly test every single custom mod pack in the world, and I would not expect you to even if it was possible. But what I do want is for my server and my single player games to run as smoothly as possible, and that simply is not the case the last few months. And the issue of incompatible on a default install is just sloppy. Its a pretty glaring oversight that's pretty easy to catch and even easier to fix, and it should have been.
If you don't want to take suggestions and make procedural changes I guess that is your choice. I suppose you could even ban me, which again would be your choice, and I am all for having the freedom to make choices. But understand that stuff like this forces choices upon people, such as getting pressured to remove the Technic platform altogether and going with something else. Especially when this thing breaks in the middle of a scheduled competition. That's not a choice I want to make, but I also don't want 500 pissed off users.