Problem reconnecting to WiFi after sleep with El Capitan

Please test after taking each of the following steps that you haven't already tried. Stop when the problem is resolved. Back up all data before making any changes.

1. If possible, test on at least one other network, such as a public hotspot or the hotspot created by a mobile phone. Some Wi-Fi routers are not fully compatible with some Apple devices.

2. Make sure the network is on the preferred list by following these instructions. It's important to read the article carefully, as it's the starting point for any further efforts to solve the problem. If you skip any of the steps, the problem may not be solved. Make sure the box marked

Remember networks this computer has joined

is checked.

3. Follow the instructions in this support article under the heading

Symptom: After restarting or waking from sleep, my computer might not connect to the Internet

4. Reset the PRAM.

5. Make a note of all your settings for Wi-Fi in the Network preference pane, then delete the connection from the connection list and recreate it with the same settings. You do this by clicking the plus-sign icon below the connection list, and selecting Wi-Fi as the interface in the sheet that opens. Select Join other network from the Network Name menu, then select your network. Enter the password when prompted and save it in the keychain.

6. From the Location menu at the top of the Network preference pane, select Edit Locations. A sheet will drop down. Click the plus-sign button to create a new location. Give it any name you want. In the new location, set up the Wi-Fi service with the same settings you used before. Click Apply and test.

7. Launch the Keychain Access application. Search for and delete all AirPort network password items that refer to the network. Make a note of the password first.

8. Repair permissions on the startup volume.

9. Turn off Bluetoothand test.

10. Reset the System Management Controller.

11. This step shouldn't be necessary, but has been advised by Apple Support in some cases, apparently as a workaround for a bug. Open the Energy Saver pane in System Preferences. If applicable, click the padlock icon in the lower left corner to unlock the settings. Enter your administrator login password when prompted.

Select the Power Adapter tab and uncheck the boxes marked

Wake for Wi-Fi network access

and

Enable Power Nap...

if present. Then, if the computer is a MacBook, select the Battery tab and uncheck

Enable Power Nap...

12. Reinstall OS X.

Same problem, Macbook Pro 15" mid 2015.

However it only appears to affect Safari (and perhaps other Apple apps, as you mention Mail).

My other apps, e.g. Slack, reconnect without issue.

Sometimes (only sometimes) closing and reopening the tab in Safari helps (reloading the tab does not help).

Sometimes opening a new tab and trying to navigate to an arbitrary website does not work.

Definitely an Apple bug, and I hope they are working on a fix.

As for the other reply that is suggesting to reinstall OS X: thanks for the advice, just dying to waste all my time.

Just to update this, I confirm that even after the latest "WiFi stability issues update", at the OS X version 10.11.2 (15C50), this problem still continues.

The only way to get connectivity is to turn WiFi OFF and then again ON after waking the Macbook from sleep, pretty much every time.

I was able to fix my WiFi reconnect-after-wake issues by deleting the /Library/SystemConfiguration directory from my system, and creating a fresh location at System Preferences -> Network.