I found the same with one of mine!! I knew that they had an award for two different things and could only find one on the search when searching by name. It turns out that when the gazette issue I needed was scanned to generate the searchable text it made an awful job of it.
I did find the entry in the gazette eventually but I had to go through the issues dated near when I thought it should be page at a time and read them very carefully. I found the search date totally by chance. William Harvie Thomson was a pilot (and the record that appears on search is for the polar medal in 1953) and his DSC in 1944 doesn't come up. However.... I discovered that, at the time, Flight magazine published lists of awards to air personnel and they also have an on-line archive. The publication in Flight was early July 1944 so I was finally able to find the Gazette record in mid June 1944.
Since you have an award date for the BEM of March 1941 you might be able to find it by hand. I did have a play but it wasn't coming up on any of the issues I looked at (searching for "British empire medal" got the correct section). Good Luck