From the cross-sectional image, it can be seen that some solid bodies are overlapping with the fluid region. I guess these solid bodies may have some problem with themselves, or while connecting with adjacent bodies. It's a bit difficult to understand the reason of failure without taking a close look at the model? Will it be possible for you to send the archived AIM project file (.wbpz) so that I can investigate this issue? I will send you a secure transfer link through email for uploading the file.