Yealight Lightstrip Plus Not connecting to router


I have 2 yeelight lihtstrip color 1S models + 8 yeelight 1S bulbs in my network working fine. After the WIfi upgrade everything still works except the 2 pcs of Yeelight Lightstrip Plus models.
They will not connect to the router.
The network is 2.4 GHZ, the devices are reset according to registration process, the Xiaomi home app discovers the lightstrip plus and starts the registration process, App connects to the Lightstrip plus and when the connecting to the router starts the progress is slow and in the end “connections timed out”.
I have also tested with Yeelight app. Same result

When I go through the same process in the same network with the same devices and procedures but using the lightstrip 1S model, the registering process works flawlessly.

Why is the Plus not connecting and the 1S is connecting?