I/O is frozen on database DBName. No user action is required
It sounds like you're using Azure Backups for SQL Server or Azure SQL Managed Backups. This is causing the I/O freeze and resume messages as it uses VSS and the SQL VSS Writer to perform the backups.
This type of backup causes issues with native SQL Differential backups (see here), with the solution being to either stop performing your native backups or stop the Azure backups.