Time machine backed up size keeps increasing
There are some details missing from your question, but here's my guess based on what you've said:
The &quot;factory reset&quot; probably looks like a first-time backup to Time Machine, and so it is backing up your entire HD/SSD. If you back up tomorrow, the amount of data will probably be much less.
In other words - this may not be an issue at all - simply Time Machine doing what it was programmed to do.