@MILOUD You could backup the current configuration and factory reset modem, and update it again. (Try downgrade the firmware before quick set up, so local update the firmware without internet...

@Amromnia If it is still under warranty, you might ask support to replace the modem. Thanks.

@jemma867 It is very likely VR400 could not hold so many clients. I see you mentioned there are several wireless access points connected to VR400 via Ethernet as well and maybe you could completely...

@tkay Have you tried a factory reset on the ADSL modem? and you could also consider subscribing higher bandwidth from internet provider now, less than 1M/s is quite unacceptable for working at home,...

@SalamAbz I think the retailer sold you the ancient stock since D50 had been end of life for quite a long time. Since you just bought it, if I were you, I would argue with them why sold me the old...

@Nely Hey, you can have a look at the following setup videos: https://www.tp-link.com/en/support/download/tl-wr940n/#video