I had a similar issue.
When I 'woke up' my TP, I would have to re-enter the security code and/or toggle WiFi off then on again.
It wasn't every time I restored from sleep, but it did happen a lot. Didn't matter if it was my home router, my friends router, or one at work.
It last about a week... then it stopped.
I can't say for sure if this stopped it or not, but around the time the problem went away, I started to use Shutdown Scheduler to power my TP down every night.