Houseplan, and Coastline. More info please.
If Jeff's advice doesn't cure the problem.
Are you talking, 2019 Deluxe, pro, or Platinum. are you using the computer between leaving TC open but unused, and starting again. Or are you just leaving the computer unattended. Are you leaving it in wireframe or render mode. 32bit or 64 bit. how much memory (windows 10 can be power hungry). what file size (uncompressed). If left unattended, could an antivirus be kicking in (scanning) and upsetting things. There are probably more questions, but that will do for now. A proper test may require a sample file but not yet.