Im new to Partitioning so excuse my ignorance.

From what I can see these are real partitions. There is a file for each partition with partition function and range defined.

As a...

The original problem was caused by an update statement in an ETL SSIS package.

I narrowed down the cause to any update statement either in SSIS or SSMS

There are about 30...

There are no triggers on the table. The columns being set to null do not have any defaults and are not calculated from other columns.

Nothing makes any sense how this...

I have just run a checktable and it returned no errors

Any updates will set these columns to NULL or the record being updated

Even this

Sales set row_update_datetime = getdate() where...