Hi Rescri,
Welcome to the Apple Support Communities. I see you're running into an issue using the Cycle function in GarageBand.
Since the ruler looks different compared to the normal Cycle bar and it doesn't seem to be behaving in the same way as the Cycle function, it sounds like a different function may be enabled. Are you able to drag the ends of the bar you see on the ruler to shorten or remove it? When you do, does this resolve the issue?
If you're not able to drag or shorten the ruler segment, try pressing C; this will toggle Cycle off. If you find the same thing is happening after toggling Cycle to off, that suggests a different setting is causing this: GarageBand for Mac: Use the cycle area
Also, to clarify, does this happen in other projects, or just this one? If it's happening in all projects, try quitting GarageBand and then click Apple menu () Restart, and test again.
I hope this helps get you started.
Cheers.