Xfinity Internet keeps dropping and reconnecting several times a day

For couple months, internet service (800 plan with MG8702 modum/router) keeps dropping out.  it stays disconnected for several minutes, sometimes up to 30; then reconnects.  I've troubleshot with Motorola who says it's an xfinity problem.  Spent several hours with xfinity in chat and on the phone support and have tried all troubleshooting options, changed out cables and splitter; but nothing fixes the problem.  xFinity default is to say a technician needs dispatching, but i live in a highrise condo building and have no control over wiring coming into my apartment. Looking at the forums this seems to happen to many people, has anyone come up with a valid fix?