HI Charlie @KingFisher78 ,
Although I don’t know exactly what happens, it looks like a classic case of ye good ol’ double Vertices, maybe combined with some inconsistent Normals. It is almost certainly not because of a Blender Version difference.
So, do what you should always do, when running into problems during Modeling: (in Edit Mode) A, to Select everything (all), then M > Merge > By Distance, followed by SHIFT+N, to re-calculate your Normals. (In some cases, Merging can leave you with wrong Normals, so do the Merge before trying to ‘fix’ the Normals.)
If this doesn’t help, the problem may be in one of the Bevel Modifiers, but I actually doubt that.
