I have also tried Chrome, Edge, and Firefox. Same result with all three on my computer. Everything works on the onx site, but the map wont load for Terrain X and the page stops responding. I've logged into onX on someone else's computer and terrain x worked.
I've had the same issue for the past month. Contacted OnX support and did everything they recommended, still not working. I was told that I would be contacted once this was fixed on their end. I'd recommend submitting a support ticket so they can gather more info on the issue.