I’m having two issues and our GIS folks can’t explain it, having little experience with rasters than vectors, and none with ‘Combine’. I am working with .asc and/or .tif output files from FlamMap. In the past, I've used Combine a LOT to help assess outputs. It's been about two years since I did this and, in the meantime, ArcMap and FlamMap have both received upgrades. Here's what I'm getting (I've now spent close to 6 hours trying to figure it out):
It's possibly mangling different filetypes. Perhaps try throwing them into a geodatabase which might manage them more effectively, then trying those gdb rasters as inputs.
And thanks for introducing me to the Combine tool!