No tags available

we have a strange case, what we catch twice already. Yesterday afternoon and today in the morning.
In logs are look like “No scan class information found for tags. warning”.
In the designer, you can’t see any tags either. When you try pulling tag tree it open with sand clock and nothing happens for about a minute. After it starts work again.
All clients application is frozen of course too.
Any ideas to where it can be related to and how to fix it?