First, I'd be looking at getting onto a newer SP for SQL 2008 R2... that thing is pretty old and out of mainstream support.
Next, I'd be asking a few questions:
1 - when did this start happening?
2 - how often does this error come up?
3 - is there a pattern with the error?
The first question helps address what you are looking FOR. If this worked in the past without issue for a while but suddenly has errors, the problem is that something changed. Determine what changed and undo that change (my guess - .NET was updated in a windows update). If it has always thrown this error or you are certain no changes happened on the server before the error started being thrown, are you on a compatible version of Windows for SQL 2008 R2?
Question 2 is more to identify if you can do a work-around to the problem. If the error happens on average once every 2 weeks, you could implement a short-term workaround while you try to solve the root cause by rebooting the server every week.
Question 3 is to see if MAYBE there is a scheduled process that is causing it to crash. This may be something like an antivirus scan locking the database files causing it to crash OR a SQL agent task that is causing the crash.
Seeing a STACK DUMP in the SQL Server Error Log though makes me think that the problem is most likely caused by either SQL Server 2008 R2 running on too new (or too old) of a Windows Version, or you need to install a newer SP to fix a known bug.
My next steps would be to replicate the server as closely as possible on a test server, replicate the stack dump, install newer SP's and/or update SQL to a supported version (2017 or newer). Do this in test so you can make sure the problem is solved AND no new problems crop up and then repeat in live.