Hi, and welcome to the forum. Sorry it's in such unpleasant circumstances.
Without knowing details, it's hard to comment on what contribution the Loxone hardware is making to the wide range of problems you're having. From what you say though, it sounds more likely that your installer is responsible for at least most of the issues.
If you don't consciously figure out exactly what the problems are first, then you're risking tearing everything out, paying for new stuff, and then still having problems. Since you're going to legal route with your installer, I'd consider getting another installer onboard to analyse what's actually gone wrong and to determine what needs to be done to rectify the situation. The costs of this should be claimable as part of your court case, since you're generally entitled to get independent advice in such circumstances.
If you're happy with their work, you could then engage the new installers to rectify the problems. If they determine that the Loxone hardware is at fault, then they'll presumably be in a good position to demand replacements from Loxone. While it isn't perfect, Loxone is generally reasonably robust, so I'd be surprised if most of your issues are due to fundamental problems with the hardware and underlying software. Certainly most of the issues I've had with my own installation have been related to third-party hardware.
Good luck.