G'day and welcome aboard Ando - you're definitely in the right place.
The hex nut shouldn't come under load from drag settings as the lever pivots around it (creating lateral force only).
It's possible (though unlikely) someone's had a crack at servicing the reel and mistakenly torqued the nut.
However, it may just appear
to have rotated (especially if you're talking about a fraction of a mm).
I haven't done one in a few months but, from memory, this is normal.
That said, it might pay to snap a pic just to be sure.
Let us know how you go.
Good luck, Justin