Here's how you can fix the Internet not working issue after waking up your Mac from sleep. There is one potential fix for users, as well as a quick workaround for the problem.
The issue is a rather plain and simple one, and one that makes you execute a brilliant facepalm once you come across it. It goes like this: you put your Mac to sleep, and once you wake it up after a few minutes or hours, Internet connectivity is absolutely dead. Even with WiFi connected, things don't move a muscle. Interestingly, the issue doesn't arise if you're connected using Ethernet.
1. Click on the WiFi logo in the Mac menu bar and then click on 'Open Network Preferences.'
2. In the resulting new window, click on 'Advanced.'
3. Now click on 'TCP/IP' up top and then click on 'Renew DHCP Lease.'
4. Click on 'Ok' to save the changes.
You'll notice that your Internet will start working, but it's a temporary fix and the issue can arise again if you put your Mac to sleep and wake it up again.
Fix Internet Not Working Issue After Waking Your Mac Up From Sleep
Read through the steps first before trying it out yourself.
1. Open 'System Preferences' on your Mac.
2. Click on the 'Network' option.
3. On top your should see an option labelled 'Location.' Click on it and then click on 'Edit Locations.'
4. Click on the '+' sign to add a new location and name it anything you want. Click on 'Done.'
5. Click on 'Location' again and make sure you select the newly created location.
6. Now click on the cogwheel button and then select 'Set Service Order.'
7. Drag the network to the top which you want to connect to first. If you rely on WiFi then move it to the top, and if on Ethernet, do the same. Click on 'Ok' once you're done.
8. Click on the 'Apply' button to save changes.
Your Internet related issues after waking up your Mac from sleep should now be resolved. If the problem still persists, then there might be a possibility that you might have damaged hardware, and we recommend that you take your Mac down to an Apple Store to get things fixed officially. But if you're certain that it's a software related hitch, then be sure to follow the above steps before reaching any sort of conclusions.
Did the above fix work for you? Be sure to let us know in the comments section below.