I have a physical computer (ALIX 1.c, https://pcengines.ch/alix1c.htm) on which ReactOS fails when loading acpi.sys. The problem is that at some point the ACPICA system calls AcpiOsMapMemory with phys = 0 and length = 0 and AcpiOsMapMemory asserts phys to be different from 0.
The request is of course a bit silly and I don't know why it is done. However, it does not seem to be prohibited by the specifications (https://acpica.org/sites/acpica/files/acpica-reference_17.pdf, section 9.2.6, page 241) and MmMapIoSpace seems to be able to handle it. Therefore I propose to drop the assertion, as the attached patch does.
With the patch attached, my computer boots correctly.