I haven't had this problem but I recall a number of folks who did. Tiersten had an explanation why these hiccups happened but I can't find the thread.
Here's another one:
https://www.mobileread.com/forums/sho...t=wifi+problem
You can "search this forum" -- it's the first from the left, on top the first forum thread and see others who opened similar discussions.
From what I saw, most recommend a restart.