Found solution. Select smart view then upper right select settings then about smart view then find window that has clear cash and data. Clear both. Go back to smart view and mirror to tv should work on smart tv.
Seems after a session of mirroring later may not work after turning phone off. Restart phone and clear cash and data again in smart view. Can be done after clicking its icon. Should work ok. Has for me.
Why it does this after android 10 update dont know. No problem with android 9.
For now this is the work around that works for me. Clear cash and data in smart view.