corrupted data in filestream table We started to observe a strange behaviour in out filestream table. 

We have a couple of records that in field with data we have 0x or 0x000...
In audit trails data we have found that these broken/empty bytes are stored on insert, so we started to investigate our insert statements (by linq to sql/stored proc executed by ado.net) and found nothing.
But what is more strange, in the audit trails we have found a few records in which the data is correct, but no records with the zeros, which are stored in real table. It looks like the data was changed without the update statement. 
We never disable the audit trails triggers on production database so each and every change should be logged.
It looks like these records got corrupted in other way, but we cant google anything and have no clue how to debug this situation properly. 
We have checked SQL Server logs, Event Viewer but can't find anything.

Can anybody suggest any hints? We are completly stuck at this moment.
There are basically 3 options:


An app or query is changing the data
Storage is becoming corrupt (which can be due to the OS, HW, storage, etc.)
You've hit a bug in SQL Server


It sounds like you've ruled out #1 (although I'm going to come back to that in a minute - but let's rule out the other stuff first.)

To start ruling out #2, run DBCC CHECKDB on all your databases. I know, you're worried about the filestream data, but it's possible that you're starting to experience corruption in other parts of the database, too. Check all of the databases for corruption, and if anything pops up, stop troubleshooting filestream and start troubleshooting the bigger issue instead. Here's my corruption troubleshooting checklist.

To start ruling out #3, open a Microsoft support case. It's $500, and they work the problem with you until it's done. (Normally I'd say to patch SQL Server to the latest cumulative update (CU) first, but I don't think I've seen any filestream corruption issues in there.) The MS support case may not be a fast fix, but I'd wanna get that process started sooner rather than later. Because filestream is a bit of an edge case feature, it's entirely possible that you've hit a bug that other folks haven't hit yet.

Those two are pretty quick - so if they don't turn up anything, then it's time to refocus on #1 (which would still be my lead suspect.)