I'VE FOUND A WAY TO RECREATE THE BUG!! :D
I really don't know if it's the only way, but it's a way. At first, I teach a bot to get fertilizer once and plant it once. Then I add the repeat functions and let the program run once (without adding the forever loop). After the bot stops, I use teach again and add the forever loop to the program. If I let the bot run now, it get's one fertilizer (so it skips the first repeat loop) and plants one fertilizer. After planting the fertilizer, it get's stuck in the repeat function like the image above.
By using this set of action, I managed to break 4 bots in a row, so it's very reliable. Because of earlier testing I think it should work with any set of actions, not only with the fertilizer. I'm not sure if it only breaks with the forever function the way I did, but it's a reliable way to do it!
Good luck!