We are using Oracle 12.2 standard edition.
I used Oracle SQL Developer (Tools->Monitor sessions) to monitor the sessions which are waiting for several minutes. I see the following waits.

How to proceed further ?
The file is not available in database with no = 201
select file#, ts#, rfile#, status from v$datafile;
1 0 1 SYSTEM
2 1 2 ONLINE
3 2 3 ONLINE
4 4 4 ONLINE
5 4 5 ONLINE
6 4 6 ONLINE
7 4 7 ONLINE
8 4 8 ONLINE