Content type incorrect in application (EPiServer.Core.TypeMismatchException)

Hi,

Version: Commerce 11.8.5
Setup: Admin, front1, front2, front3

We had an (2, technically) incident where all the content (Products, Variants, Categories...) in Commerce reverted back to its core implementation: Castle.Proxies.ProductContentProxy (etc) instead of our custom implementation, giving us EPiServer.Core.TypeMismatchException all over the place. Perhaps notable is that only Admin & Front3 seems to have been affected.

This was not preceeded by an IIS reset, App Pool Recycle or anything else that I can find in the System/Application logs; everything looks fine as far as I can see (checked around the time of the first occurance of the error +- a couple of hours.

The database looked fine which made us perform an IIS RESET which fixed the issue, however a lot of damage was already done by the time we realized the issue. 

I'm just wondering if this is something known, our best guess is that it might be a bug in EpiServer. I haven't been able to find any details on issues that matches our issue on the forum, or anywhere else for that matter.

Timeline:
Deployed 11.8.5: 2018-08-15
...
First occurace on front3: 2018-09-08 23:37
Fixing IIS reset: 2018-09-09 22:20
...
First occurance on admin: 2018-09-12 13:33
Fixing IIS reset: 2018-09-13 09:21

These are the only occurances.


Any ideas are appreciated.
Thanks,
Fredrik