I would try rebooting the iPad as the initial troubleshooting step as well. Since you mentioned that you are using an Asus router, have you made sure to Enable Multicast Routing in the router settings? We have sometimes seen this setting affect Roon Remote connections as mentioned in our Networking Best Practices Guide.
Glad to hear that rebooting the iPad resolved the issue! If possible, I would also take a look at the multicast settings I mentioned, as it may help and if it does I would be interested in knowing this info.
The Muticast Routing settings should affect both. We are looking into a few similar reports where just the iPad has issues connecting to the Core, and I am curious to know if multicast routing helps with this issue.
Thanks for the follow-up! Do let me know if multicast routing appears to have fixed the issue over a longer time-period as this is a good data point for us to have. Thanks!