When using the clone command in command blocks the area can officially not overlap. But this is possible when the command block is on the edge of the clone area. In the case of the command block being on always active the command block will now indefinitely duplicate itself until the world-border is reached.
The issue should be repeatable using the screenshots.
This is an issue because when building large structures or farms the clone command is really important and People can accidentele ruin their build because a command block indefinitely duplicated itself and a wall.
Thank you for your report!
We're tracking this issue in MC-245602, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki