@Stathis Tapinos -

When you are in the Miro dashboard, do you see multiple team icons in the left vertical edge? If so, can you confirm you are in the right team where those boards were created?

Are you able to access any of the boards by locating their URLs from your browser history and accessing them directly that way?

If not, then a Miro support request might be your best bet: Submit a request – Miro Support & Help Center

Kiron

Thank you, Kiron.
Interestingly enough, the multiple team icons have now appeared in the left vertical edge. Admittedly, this must be a relatively new function, as I had never noticed before. In the past, all my canvases were not spilt into teams. Anyway, thank you for your help. 
Regards, 
Stathis 

For context for all readers, this “team switcher” vertical bar is always present as it

• is the only way you can switch between teams (if your Miro account profile is a member of more than one team, or has any relationship with a board outside of your team, e.g., someone added you as a viewer to a board in another team) 
• and it is where the “Add teams” icon is.

In this example, I was only a member of one team, but then I was added to another team and now I can switch between the two dashboards: