The blog entry Revisiting the Intel 432[0] and the cited paper Performance Effects of Architectural Complexity in the Intel 432[1] discuss the compiler issues.

[0] https://bcantrill.dtrace.org/2008/07/18/revisiting-the-intel...

[1] https://dl.acm.org/doi/pdf/10.1145/45059.214411

I do recall some discussion about combination of really bad code generation combined with some ridiculously bad design decisions (I think it might have been total lack of cache?)

All I know is the Wikipedia article references a crappy Ada compiler whose lack of optimization made it run slower than a 286:

https://en.wikipedia.org/wiki/Intel_iAPX_432