This strikes me as entirely plausible. The Debian main component is huge. In a recent sync I did for Debian Buster it contained 56890 packages. By comparison a sync of Ubuntu focal main contained just 6090 packages (that is just the main component, I don’t know off the top of my head how big it gets if restricted, universe, and multiverse are also included).
Can you post the exact error message and/or backtrace?
We have been observing this for long syncs in general where connections are being reset.
I need to bring this up with the core Pulp team, and any information you can give me will help.