when I set the keyframes in LRT 6 (12) and start to edit the images in LRT, it sometimes happens when applying the settings to the next keyframe that the next keyframe hangs up. The settings are then reloaded over and over again, you cannot continue working.

Is it possible that you have Lightroom open on background and in the lightroom settings you have set it to automatically store settings to Xmp? Please check and turn that off! It's also explained on the install page : https://LRTimelapse.com/install

Thanks Mr. Wegner, but there is no Lightroom open in the backround

Ok, I was guessing, because I don't have more information from you.
Could you please use the latest beta (it doesn't make sense to work with outdated betas).
Then try again. If the problem reappears, post the log here (info menu) and describe the steps to reproduce that.