Hmm.. I had a similar problem.
Have you tried disableling the fire walls on the second PC. Aslo check that there is no other software running on the second PC which needs internet access but you do not need to run as this can cause problems, such as windows update or anti virus updates.
If the connection drops again, check with task manager to see what is running. There could be something here causing the problem.
I have also disabled windows bit defender on my second PC for good measure. And now no connection drops.