@sparklemeplenty 

When I try to resize an art board, it returns back to its original state when I release the edge.

When you mention artboard, are you using the Adobe XD or Sketch plugin app with Miro? 

If you are using one of these apps, have you tried reinstalling the app?

When I delete something, it goes away for a second, but then reappears.

Is this for any object or just objects created using a plugin?

If you are using a browser, have you tried

1. clearing the browser cache
2. or an incognito/private browser window?

If you are using the Miro desktop app, have you tried resetting the app data?

You may also want to open a Miro support ticket.