Yes me too, from iPhone and Safari on Mac.
As a workaround, I would use Wikipedia. Not for proof, but to help with planning. Look for blue links on the Wikipedia “hillforts in [your county]” webpage, and check each to see what it says about it the dates of each. It’s highly likely if Wikipedia has heard of it, the Oxford Uni Atlas will have too. Then it’s a gamble on the accuracy on Wikipedia,
Disclaimer: I’m not a member of ChallCom. I don’t have the certain je ne sais quoi.