After contacting support, they somehow enabled the server for me again now resulting in a permanent restart of the WEB UI after each trade. They requested several files which I generated and sent them. They were just to confirm that this is a problem but didn't came up with a solution. It's probably worth to mention that I am using gunbot on a Mac (relative new M1 Mac Mini) and version 28.6.7. As they had no solution, I completely reinstalled version 28.6.7. again just to get a license error. I then replaced the config.js with the one of the 'broken' instance and everything seem to be working again.
However, after a few hours (and lost of quite some money) the bot stopped working and after restarting the original problem is back. The UI starts again over and over.
Quite disappointing.
Especially because I paid twice for gunbot. I bough a 'lifetime' license a few years ago from gunbot.shop (the 'official gunbot reseller') for quite some BTCs by that time. There is a post in this forum that people who bough their license in this shop some time ago should contact them. Which I did several times in several ways (also using the reseller website) but never got any answer back. So keep in mind, lifetime is indeed not lifetime.
Again, very disappointing.