Internet keeps disappearing, up to 5 times a day

Since the last maintenance of KPN July 19, internet has been disappearing from all our devices at home. For example, the internet would work on TV, tablet but not my phone, or it would work on my phone but not on tablet or my partner's phone. We solve the problem by rebooting the modem. However, we have been rebooting the model at least 5 times a day since a week. This is not normal. This problem started the day after KPN carried out maintenance (they sent a text). How can this be fixed? To me the problem is linked to KPN maintenance (something happened). I am already paying for a service and do not want to pay a technician. KPN must ensure their service works.