I've been working on that exact problem for the last couple weeks. My solution for now is rt patch and a dedicated cpu core for rt tasks. This already works pretty reliable, but I notice small delays from time to time. I gather from the article that my problem might be page swapping. I don't know how to improve that, yet.
Also for anybody working on rt problems: I highly recommend the stress-ng tool for stress testing and finding bottlenecks of your system.
Does this mean you have to use apt-get to get the deb version again? Or is there an even more complicated command? I'm wondering what happens for the other Ubuntu flavors. I'm usually running Kubuntu.