The issue is most likely the app. Currently, it does not work with v7.3 of RutOS, but our RnD is working on fixing it.
If you do not use RMS, then the only recovery option will most likely be connecting to the router via a LAN cable. However, if you do use RMS, you should be able to downgrade to v7.2.7 and connect via the app that way.
We apologize for any inconvenience caused.
Best regards,
DaumantasG