While upgrading Workflow Server from 8.3 to 9.1.1, some of the workflows running were stuck at 'SDK Script'. Is this an expected behaviour and if yes then what is the solution to this?
Do you have multiple workflows with the script activity running simultaneously? I have this problem when running script activities in workflows that can run in parallel and always find a way to ensure they run one at a time. You can use a schedule and for each loop as a work around.
This definitely isn't intended behavior. Do the workflows end on the script step, or are they in a constant running state?
The scripts are throttled on the server for overall performance reasons. As such, it is possible that slower scripts (from other workflows) that take longer to run are causing your script in the current workflow to get queued up. You may be able to see the currently running ones under Advanced Diagnostics\All Tasks in the Workflow Administration Console.
Do you have any scripts executing long running operations like OCR, or launching other executables?
Note that there isn't a lot of information to go on in your post and this is just a guess based on the default configuration and expected behavior of a Workflow Server. For proper investigation of the issue, you should contact Tech Support.