I also have this problem. the iPad Pro 2018 12.5” (plus cell) when it sometimes wakes from sleep, is connected to the router but NOT able to get to the internet. Also, it will NOT connect via LTE either. The ONLY fix is a hard boot. After the hard boot, immediate connection to WiFi and internet.
It it seems that it only happens towards the end of the day. Battery around 50%. After its charges all night, I don’t have trouble again until the next evening.... when the batter is again around 50%.
turning OFF WiFi auto connect works. When the ipad wakes up, I manually connect to the network. No problems getting to the internet. If the iPad doesn’t go into sleep mode, no problems with dropping or not being able to connect to the internet.
my home network is not the issue. Every other device (apple or otherwise) we have works fine. Router is apple AirPort Extreme. Service is AT&T.
i think that there is a power management bug on this iPad.