Any luck tracking this down? Are you using the PBS runner or a DRMAA one (and if DRMAA what DRM)?
Are you using the local job runner for anything? If yes - it may be worth splitting the local job handling into its own handler to eliminate that as the source of the problem.
Are you using Postgres - and if yes have you enabled the option database_engine_option_server_side_cursors = True?
If you have some time, a test setup and can reproduce - it may be worth running with use_memdump = True in galaxy.ini - I am forget what it does exactly but I feel like I have used it to track down memory problems in the past....
Long story short - I have no clue none of the changes we made that release come to mind as possible culprits - very sorry.
-John