Timmy has two upgraded Windows 10 laptops, and when he tries to move files around, the computers will slow down and ultimately crash. Leo says that Operating Systems have an index of all your files, and it could be that the indexes on both computers are corrupted. The indexes will need to be rebuilt. Click on the Windows key and type Indexing options. Select the rebuild option. It will take a while, so it's best to do it before you go to bed. Also, make sure the folders that Timmy is trying to move haven't been excluded. There's a button and listing for that.
The other option is that the computer SSD drives have started to go bad. That is unlikely but possible. Windows Defrag tool has a TRIM option and defragging the SSD drives will do that. Outside of those two options, as unlikely it is, the controllers could have gone bad as well.
You can also look for a copy utility called "robo copy" on your Windows machine and use that instead. It's a command-line utility, so google RoboCopy and Windows 10. It's much better to copy a lot of files than Windows regular copy utility.