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Interrupt disable time is obviously greatly affected by the speed at which the processor accesses instructions and thus, the memory access speed. In this case, the hardware designer might have introduced wait states to memory accesses, which affects overall performance of the system. This may show up as unusually long interrupt disable times.
Finally, because the interrupt disable time is also affected by the overhead caused by enabling trace calls, enable tracing only when tuning or debugging your embedded application, and disable tracing when you are finished or when you want to measure interrupt disable time without any tracing artifacts (e.g. OS_CFG_TRACE_EN in os_cfg.h).