I might be a little late to voice my feedback, but I just hope that the CM or some devs will come across this:
First of all let me point out that I really really like Stellaris. I've put more time into the game than I should have. To me, it is by far the best sci fi strategy game there is. Additionally, I fully support the way that PDX keeps on developing content of games well after their release. This is something not seen in most games and it is what keeps my hopes up, that Stellaris will keep on improving and be an even better game in the future. However, I strongly agree with all of the previous posters who think that the latest DLC release was not okay.
I do understand that adding new features will introduce a lot of bugs. I also do understand that all QA on this world cannot get rid of all of the bugs. There will always be some leakage that the player base will find and which will need to be addressed in future patches. Regarding PDX's DLC model, this is perfectly fine. If you buy a DLC, just like when you buy a new game, you should expect some bugs. This is normal an will be fixed in the following weeks.
However, this does not excuse the recent game breaking changes. Its not just new features that are broken. Over the past DLCs, old features were broken. Repeatedly. Content which customers payed for, which was functional at some point, was broken while introducing new features. Meaning that not only did those who bought new DLCs not get a bug free experience when enjoying new content, but those who didn't buy the DLCs had to watch while the features that they had paid for became worse. This is what bugs me the most.
If all that had happened, was for PDX to release a broken DLC, which didn't affect the rest of the game, I simply wouldn't care. I simply would not have bought the DLC on release, waited a few weeks for all of the bugs being ironed out, and join in afterwards. But that's impossible. Yes, you can currently roll back to version 2.1.3, but the same problems apply to that version too. While it did improve some things, it broke others. There simply is no way for me to enjoy a stable version of the game, even though I have thus far spent more than 100€ on the game.
In all of software development, you should have regression tests. This is even more true for a game like Stellaris where the devs themselves claim that they want to keep on improving the game for several years after release. Adding new features doesn't have any benefit, if you keep on breaking core components of the game. Yes, regression tests can be annoying. Coming up with test cases for tiny features etc. isn't what devs like to do. But it is necessary. Once you have identified a test case for a given component of your software (e.g. running a few games in observer mode to validate your AI), you write them down and you pay someone to repeat them for newer versions.