I've been experiencing this issue for several months, and it doesn't seem solved in the recent 0.14.0 update.
I suspect there might be more than one issue: sometimes we can work around it by restarting Minecraft on the server device, sometimes on the client device. Sometimes turning WiFi off and on is necessary (again, it seems to vary on which device this is required).
Today I replaced our BT Home Hub with an (old) Apple AirPort Extreme router, but sadly that also doesn't seem to have fixed the issue.
Afraid it still appears for my family in 0.14.0.