New iPads constantly dropping wifi

Update. It seems there is something with IOS 18 that didn’t cause the problem but made it apparent (if that makes sense). A couple of years ago we received a new WiFi router and it was set up with its own WiFi network. However, I neglected to change the name of the Apple AirPort Express that I used to extend the old router network and continued to do so with the new router network (to the living area;) its name remained the same as the old network. It seems with an updated AppleTV iOS and new iPads, with iOS 18, having two networks with different names was causing an issue (not sure why as I thought having a couple of different network names must be a common situation with WiFi extenders and the device should join the stronger signal as you move about - am I wrong on this?) For me the devices would constantly drop the old network and then join again after a second or two. However, Apple devices with iOS 17 (my old iPad and MacBook Air didn’t have the issue; they were stable on the AirPort Express network with the old name and didn’t drop it. I solved the issue for the new devices by renaming the new router network and used the same name for the AirPort Express network. Haven’t had a drop on WiFi since. Not sure why the older devices were ok. I would have an old iPad and a new iPad side by side and the new one would have the (Airport Express) old network name disappear, the cart wheel spin for a second or two, then the network would reappear again while the old iPad just sat there and remained with a constant network. At times the new iPads were dropping the network every 30 seconds or so but for only a second at a time.