I was not able to repo your issue while adding a custom field (using the Project Picker field type) to our JSM project's request type form. Did you evaluate your effected request type form fields setup? I assumed you already there.
One other issue is that even it works, you need to know that Customer (may not have access to the project listings), thus it will results in an empty list.
Hope this helps.
Best, Joseph Chung Yin
Jira/JSM Functional Lead, Global Infrastructure Applications Team
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