We also have this problem and we are not alone with it. The Swisscom technician recommended that we switch to the latest Siwsscom hardware and only use Swisscom hardware (WLAN access point and PLAN), which we did. Until today 21.09.2019 the problem was not solved.
on the swisscom internet box routers:
nope, that's not possible
via third party routers:
yes, that exists. But than you need to manage each client (==computer) individualy