Upgrading an existing GemStone database to use Unicode requires careful planning and execution. There are significant differences from conventional strings that affect how strings (Unicode or traditional) sort and compare.
[Note that installing Seaside in an existing GemStone database will upgrade it to Unicode.]
The bug note for issue #46694 addresses some of these.
"When changing an existing application from the standard mode to Unicode Comparison Mode, you must take steps to ensure any structures relying on comparisons are rebuilt; indexes on strings must be rebuilt, sorted collections on strings may need to be re-sorted, and dictionaries with string keys may need to be rebuilt."