By adding another data item which came from the package, The test did run successfully.
It is weird that it shows error when run from the migrated reports.
Wonderful. Now we know the issue is due to something specifically in those reports. I still think this is going to eventually lead us to my original answer in this post.
I think there are multiply things happening:
1. There's local processing in your report (that's fine)
2. The way your query is designed, it's trying to process the date returned by to_date()
3. There's more processing happening on that date, and it doesn't like comparing a character to an integer (something which Cognos "allowed" in some cases in the past)
It's not so easy to trouble this part without having the report. If you're able to post the report specs and the SQL generated by the query, I can take a look.
I don't think you will find a solution where these reports upgrade without any modification, but at least if you know the root cause you could make a more informed decision.