I/O is frozen on database . No user action is required. However, if I/O is not resumed promptly, you could cancel the backup.

Error: 

I/O is frozen on database <database>. No user action is required. However, if I/O is not resumed promptly, you could cancel the backup.

I/O was resumed on database <database>. No user action is required.

DB Version: MS SQL Server 2016 SP2.

Scenario:

Every day we have observed the above error in one of our production database. When I retrieved the backup history of a database, the specific backups are created every 6 hours of interval of time. At that time all the application jobs got suspended for time being. This was a daily complaint we received from application team. 

First, it starts with an I/O freeze message on all databases at the same time.

I/O is frozen on database <database>. No user action is required. However, if I/O is not resumed promptly, you could cancel the backup.

Then, after 5 seconds I/O is resumed on all databases.I/O was resumed on database <database>. No user action is required.

This error was due to VEEAM backup. As our whole infra backup taken through VEEAM. This has been scheduled for every 6 hours and had removed the schedule during business hours.