It's not frozen for me. I don't use it often but just tested it. My iPad is at OS Level 14.6. I tested first with the network turned on - which worked and could search and find different shares. Then I turned off the network to see if I could break the app. The app responded fine when offline. Last I stopped the app then restarted with the network turned off from the start. Still worked fine as offline.
I also logged into my account using the Soundmondo app and that all worked fine for me too.
Soundmondo is designed to work with many current generation synthesizer products. It may help to document as many details as possible (like which keyboard you are connecting to) as well as your iOS OS version, Soundmondo version, etc.
It would be difficult for someone else with a similar sounding issue to match up anything other than the most highest/general level of facts (a "freeze" with some version of soundmondo on iOS with some yamaha keyboard).
Even the "freeze" is not well defined. The app has many screens - any particular screen which is unresponsive? What were you trying to do that wasn't working? I.e. which button/control/etc. in the app was being pressed and was not responding?
It's good that it's working now. Someone else having a similar problem may benefit from some more historical detail.