@Maclav - Without knowing anything about what is on the board that won't load, it's hard to say what the reason is for it not loading. However, my guess it that there is something "stuck" in a cache.

I would suggest duplicating the board and see if you can open the new/duplicate. If that works, delete the original board and you're good to go. If that doesn't work, then I would try resetting the tablet app's cache - see the FAQs in this article:

https://help.miro.com/hc/en-us/articles/360017731633-Tablet-app#h_01F6F1CB4PXYZHC59C057VXWQK