Well I've learned the hard way that when I run out of easy answers I need to check that my assumptions hold up 🙂 So mant times for me, the assumption I didn't challenge was the one that didn't hold up.

Assuming you tried the error checking like Sergiy mentioned - I would look at a few additional items (again - just hunting for now - we don't have a root cause as of yet):

- check for any references to IDENTITY_INSERT directives in your code.

- a few additional profiling checks that might help:

select ss_id from session

intersect

select sh_id from session_hist

select * from session_hist where sh_id=-1

edited for typoes