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There is a clue in the warnings above the fatal error:

* Warning * Calculated design cooling load for zone=THERMAL ZONE 1 is zero. * ~~~ * Check Sizing:Zone and ZoneControl:Thermostat inputs. * Warning * Calculated design heating load for zone=THERMAL ZONE 1 is zero. * ~~~ * Check Sizing:Zone and ZoneControl:Thermostat inputs. * Warning * SizeUnitarySystem: ZoneHVAC:PackagedTerminalHeatPump = THERMAL ZONE 1 PTHP * Fatal * Unable to determine fan air flow rate.

The sizing results for the 23C file show no heating load, and a small cooling load (from the eio output):

! <Zone Sizing Information>, Zone Name, Load Type, Calc Des Load {W}, User Des Load {W}, Calc Des Air Flow Rate {m3/s}, User Des Air Flow Rate {m3/s}, Design Day Name, Date/Time of Peak, Temperature at Peak {C}, Humidity Ratio at Peak {kgWater/kgDryAir}, Floor Area {m2}, # Occupants, Calc Outdoor Air Flow Rate {m3/s}, Calc DOAS Heat Addition Rate {W}
 Zone Sizing Information, THERMAL ZONE 1, Cooling, 366.58315, 366.58315, 3.58480E-002, 3.58480E-002, TESTDESIGNDAY, 7/20 19:00:00, 33.37000, 1.05960E-002, 60.00000, 0.00000, 0.00000, 0.00000

With the 25C setpoint, there is no load, and there is zero outdoor air, so there is nothing to calculate a flow rate from. The PTHP flow rates are zero:

! <Component Sizing Information>, Component Type, Component Name, Input Field Description, Value
Component Sizing Information, ZoneHVAC:PackagedTerminalHeatPump, THERMAL ZONE 1 PTHP, Design Size Cooling Supply Air Flow Rate [m3/s], 0.00000
Component Sizing Information, ZoneHVAC:PackagedTerminalHeatPump, THERMAL ZONE 1 PTHP, Design Size Heating Supply Air Flow Rate [m3/s], 0.00000