I am working with the following ten landsat 8 images:
LC81340412016058LGN00 LC81350412016065LGN00 LC81350422016001LGN00 LC81360412015341LGN00 LC81360422016216LGN00 LC81360432016216LGN00 LC81370412015316LGN00 LC81370422015364LGN00 LC81380412016086LGN00 LC81380422016214LGN00
When I opened these images in QGIS with the supporting shapefiles it covered the entire state of Assam (in India). But After I tried to merge them using QGIS Raster tool the merged image did not cover the entire state. Only a small part of Assam was shown in the QGIS in the merged image.
Before merging in QGIS
after merging in QGIS