Incremental backup VERY SLOW

I just switched from TI 2010 to 2016.

I always do a full backup on an external disk, and then for one week, incremental backups. Then I switch the external disk and start all over.

The total backup volume is 1 TB, with about 2 to 50 GB per day in the incremental backups.
With TI 2010 the daily backups took between 5 and 20 minutes.
With TI 2016 tje daily backups take more than one hour,
Why is that?

I used the same settings as before and even switched the priority to normal (in TI 2010 I used 'low' all the years).