Thanks all for their feedback.
One of the problems mentioned in original post is resolved which is 'util_vol_online' option.
The error reported by BRBACKUP (BR0344E) was because .switch.log file created by BRBACKUP towards end (after #END...) was not deleted by backint.
However, the problem of semaphore file not getting deleted by BRBACKUP in 'util_vol' option is still not resolved. While the backint is waiting for .switch.sem file to be deleted, an instance of BRCONNECT operating on the very same BRBACKUP process can be observed. This BRCONNECT process does not close for long time and probably for the very same reason .switch.sem file is not deleted by BRBACKUP. It's not clear though, why BRCONNECT takes long time (over 2-3 hours).