I have a strange problem.

The k2 items view in administrator view is VERY SLOW.

This happens whenever I try to do ANYTHING with k2 items (view item, browse to any item, starting new item, saving, etc)

It does not happens with any other elements in the administrator and does not happens when dealing with other k2 elements other then k2 items (categories, tags, users etc - they are working fine and fast). I doesn't matter how many k2 items are in display in items view (even if there are only 5 items in items display, still it takes 1-2 minutes to view them or display timeout error message).

The front side of the site is working well & fast (also the k2 item display).

I'm using k2 ver 2.9 on joomla V 3.8.3

ANY IDEA what can i do ?

Try to enable debugging while you are working with K2 items in the backend, this may help to determine what takes longer time to execute the task.
Go to the global configuration> System
Set Debug System to Yes
Make sure to switch it back to No directly after you load the items.