You can clearly see the moustache from the beard come away from the face of Connor Swindells as David Stirling at 02:18
The Italian sailors in Benghazi are all armed with Mauser Kar98s. Italian troops of that period would be issued some model of Carcano rifle not Mauser.
At 19:43, Augustin Jordan's line "we're here to defeat fascism" is quite clearly ADR recorded as the sound mixing on the line is very different from the preceding and following lines. Also, the spoken line obviously doesn't match up with the mouth-movements seen on screen - at one point in the line, the actors mouth is not even moving.
At 27:22 Virgile Bramly as Georges Bergé says "No one divides us Lieutenant Mayne", he's a Captain, wearing Capitan pips.