why do some websites not load on ipad

The best way forward is to start with the simple stuff first. Try powering the iPad off completely - i. e. not just putting it to Sleep - by pressing and holding the Power button until the slider control appears. Accept the offer to switch off and then, when the iPad has completely powered down (blank screen), press and hold the Power button again until the white Apple logo appears and then wait for it to power back up.

This simple procedure cures a whole load of problems and even Apple recommend you do this at least once a week.
How long has it been since you restarted your wifi/router?

I would do this and see if you get an improvement. I've tried this several times with no luck. I deleted the wifi connection from the ipad and then signed back in. Initially I was able to view at least 10-15 web pages from various web sites without any problems.

Then the error messages started popping up again. Each time the error messages pop up I either turn the Ipad off and the back on, hitting the 2 buttons at the same time and waiting for it to fire up again.

Once it starts back up once again I can visit several web sites and then the messages start popping up again. It then repeat the process over. As I mentioned earlier my Macbook Pro which also works off the same wifi connection works fine.

Have you got auto assign IP numbers or static? Auto assign you should have no issues but if you have static numbers and have two devices with the same number, this will cause issues as well. I don't know how to find this information so I'd need some help trying this?