Why is the differential backup increasing?

Question

Backup

There is a base 1C ~ 70Gb, it's all spinning on MS SQL Server 2012. Backup is configured full - once a day, diff - once an hour. Recently, the diff has grown greatly, that is, in uncompressed form, the backup weighs about 10 GB. The transaction log does not grow significantly. On neighboring bases on the same server, this picture is not observed. From the side of 1C, according to the programmer, everything is regular, there are no special activities. Index rebuilding tasks are temporarily disabled in the database, without much effect. I ran the databases with scripts for the number of reads / writes in the tables, nothing suspicious was found, so most likely it's not 1C. I also went through the found script ( https://www.sqlskills.com/blogs/paul/new-script-ho...shows changes of a few percent. That is, there is nowhere to take big changes in difof. The logs are also silent. We also unloaded the database in dt and recreated the database in SQL without much effect. Interestingly, creating a full backup does not affect the size of the diff in any way, that is, it does not reset to zero, but grows in an arithmetic progression every hour by 100 MB.
The task was created by the master, just in case I attach the code.
Master.dbo.xp_create_subdir N'U the EXECUTE: \ the Daily \ utd ' the
GO
the BACKUP DATABASE [utd] the TO DISK = N'U: \ the Daily \ utd \ utd_backup_2017_12_19_073714_4008849.bak' the WITH DIFFERENTIAL, noformat, NOINIT, the NAME = N'utd_backup_2017_12_19_073714_4008849 ' , SKIP, REWIND, NOUNLOAD, COMPRESSION, STATS = 10
Up to this point, the database has been backed up in this way for several years, there have been no problems. Unfortunately, there are no more ideas what else to try, so I ask for help.

Answer 1

2017_12_19 is this just an example, or are the diffs on December 26 really created relative to the backup of December 19?

Answer 2

Offhand - the size of the database and log? Maintenance of base becomes - the standard maintenance plan?
Almost the same thing is configured on the production server and has been working without any questions for a long time:

EXECUTE master.dbo.xp_create_subdir N''\\bdserver\sql2008$\db1''

GO
BACKUP DATABASE [db1] TO  DISK = N''\\bdserver\sql2008$\db1\db1_backup_2018_01_04_163005_0456141.bak'' WITH  DIFFERENTIAL , NOFORMAT, NOINIT,  NAME = N''db1_backup_2018_01_04_163005_0416137'', SKIP, REWIND, NOUNLOAD, COMPRESSION,  STATS = 10