Safari v18.0 on MacOS 15.0 Page Loading Issues

I needed to complete an online claim form with Royal Mail (U.K.) for delivering a Special Delivery Item AFTER 13:00, the guaranteed delivery limit time.

Using Safari, after indicating which service I was claiming on, you proceed with Date Sent etc. After completing the first page of the claim form, I could not progress further with my personal details.

Using Microsoft Edge, after indicating which service I was claiming on, you are then asked for the unique Tracking Number before moving on with Date Sent etc.

My question is; Has Safari 18.0 got a flaw and will not display web pages properly? Why did Safari not display the box to enter the Tracking Number?

Any comments would be helpful please.