I downloaded 4 dems from the USGS with 30 m resolutions. I created a mosaic of these 4 dems, then tried to fill it but the ARCGIS 10.8 and 10.7 could not do the fill. Although, this funciton worked well before creating the mosaic. I tried many solutions but without success. I exported the dems to grid, and I changed the place of storing the output file but also without success. I created contour then created TIN then converted the TIN into raster, then it worked but with bad resolution. I am frustrated. Please help. thank you