TL-WR940N_V2_140627 - it's latest firmware for your router. When connecting a fairly large number of devices (8-9), it also requires its daily reboot, otherwise some devices drop in and out of...

Can you see some information from device about error connection?

W10 is test version for now

Are you trying router access by IP address?

UPnP feature disable in router settings.

I think that is wrong idea. You will disrupt MIMO system work in your wireless router. Wireless access may be unstable