How to find out the reason for the loss of connection between two MacBooks?

Question

macOS

Two MacBooks, between them is a Time Capsule as a router. The first macbook has Shared access to the X folder. The second macbook connects to this folder via smb using the account from the first macbook. The second laptop downloads data from the first. Many small and large files per 100GB.
Everything is fine for the first 10-20 minutes, but then the process stops. I open Finder, select Network, the first computer, the desired folder, and nothing happens. Empty Finder and "Connecting..." in the status bar. And it can stand like that for half an hour, no mistakes, nothing like that. You press the extraction icon or the Disable button - silence. Nothing turns off, just silence. Everything just hangs. Only reboot helps. After restarting everything is fine again and you can continue to work.
Where do you think the problem is? Since restarting the computer helps (the second one, of course), it is unlikely that the first laptop has a problem and it is unlikely that the router has it. So something with the second, but somehow I do not understand.