Nexus 5 - Unable to connect to Wifi after sleep mode

Since a couple of days (after we made the change to daylight savings time actually) i'm unable to stay connected to wifi with my Nexus 5.

I can find the network okay but I can't seem to connect.

I've noticed that I can connect to the wifi network after I reboot the phone (holding the on/off button for 20 seconds). But as soon as the phone enters standby or sleep mode I'm unable to reconnect to the wifi until I reboot again ..

Any ideas?