The issue here is that the particle instance modifier (pimd) accesses data from the linked particle system modifier (psmd). This data is only correctly generated when the psmd is enabled; here the design violates the modifier principle of providing valid object data (or rather DM) even when disabled.
The solution in this case is to make a custom isDisabled check for the pimd to see if the psmd is enabled. This means the pimd won't work for disabled psmd, but doesn't crash.
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