Strange, I was able to get it to work. I have attached an fds script you can try out and see. The two surface temperature devices show the transfer of heat.
Are both sides of the obstruction the same layered material?
untitled.fds
Generated by PyroSim - Version 2022.3.1208
6-Feb-2023 4:17:31 PM
&HEAD CHID='untitled'/
&TIME T_END=1000.0/
&DUMP DT_SL3D=0.25/
&MESH ID='Mesh01', IJK=10,10,10, XB=0.0,2.0,0.0,2.0,0.0,2.0/
&REAC ID='FDS6 PROPANE',
FYI='FDS6 Predefined',
FUEL='PROPANE'/
&DEVC ID='Front Surface Temp', QUANTITY='WALL TEMPERATURE', XYZ=1.0,1.0,1.0, IOR=3/
&DEVC ID='Rear Surface Temp', QUANTITY='WALL TEMPERATURE', XYZ=1.0,1.0,0.8, IOR=-3/
&MATL ID='STEEL',
FYI='Drysdale, Intro to Fire Dynamics - ATF NIST Multi-Floor Validation',
SPECIFIC_HEAT=0.46,
CONDUCTIVITY=45.8,
DENSITY=7850.0,
EMISSIVITY=0.95/
&SURF ID='Steel',
RGB=146,202,166,
MATL_ID(1,1)='STEEL',
MATL_MASS_FRACTION(1,1)=1.0,
THICKNESS(1)=0.2/
&SURF ID='Burner',
COLOR='RED',
HRRPUA=1000.0,
TMP_FRONT=300.0/
&OBST ID='Obstruction', XB=0.0,2.0,0.0,2.0,0.8,1.0, SURF_ID='Steel'/
&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=2.0,2.0,0.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=0.0,0.0,0.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=0.0,2.0,2.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=0.0,2.0,0.0,0.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=0.0,2.0,0.0,2.0,0.0,0.0/
&VENT ID='Vent', SURF_ID='Burner', XB=0.0,2.0,0.0,2.0,2.0,2.0/
&SLCF QUANTITY='TEMPERATURE', ID='Slice', PBX=1.0/
&TAIL /