Many iPad users after updating iPad Mini 2 and iPad Mini 4 from iOS 11.2 to iOS 11.3 Public Beta 1 and after the update finished, the iPad Mini can't connect with wifi. The WIFI seems to work fine as other iPhone and mac can join wifi network. The user tried Resetting the network did not work to fix WIFI issue on iPad on iOS 11.3.
However there are no updates from Apple for the fix and quite possible Apple should fix this in iOS 11.3 beta 2, but you can try below workaround/fix to check if it works :
How to fix iPad mini not connecting to WIFI on iOS 11 :
Fix 1: Reset iPad Settings
Please make sure to take backup before trying this .In case resetting network settings does not work, try to reset entire iPad, and restore it to an iCloud backup (on iOS11.3). After the resetting your iPad, it should connect to WIFI fine now
Fix 2: Revert back to 11.2
Below are the steps to downgrade from iOS 11.3 to previous versions where WIFI works fine with iPad mini.
1) Downgrade it to 11.2.5 via iTunes.
2) While holding HOME + POWER, wait for the phone to reboot and continue holding until the screen prompts to plug into iTunes. This is the restore screen.
3) Plug into computer
4) Open up iTunes and there should be a screen with "UPDATE" or "RESTORE." Choose UPDATE and confirm on the pop-up.
5) UPDATE triggers a downloading of 11.2.5 and will commence the restore/upgrade process which in this case is a downgrade from 11.3. This should retain all data on the device.
Now the WIFI should connect find on iPad mini2/3/4 on the older iOS version and please wait until Apple rolls out more stable version to fix WIFI issue.