It seems to do it pretty inconsistently, and simply removing and replacing faces works sometimes. Sometimes if I mess with a face it prevents it from beveling the whole object alltogether. There doesn't seem to be much rhyme or reason to it messing up the bevel, is this just typical blender issues or am I doing something wrong? I thought I followed it exactly like in the video.
Do you have any other modifiers enabled? It might be that the order of the modifiers is messed up. try putting your bevel modifier above all of the others. It also helps a lot to provide screenshots so we can see what's happening! hope this helps!
Consider the following before doing the bevel:
1) Remove excess vertices - In Edit mode, select all vertices and then press Alt-M (if Blender 2.83 - just M). Choose "by distance." Do the bevel again.
2) Normals facing same direction - In Edit Mode, click on the Viewport Overlays pull down menu. Under geometry, click on the Face Orientation checkbox. If across the bevel there is a combination of blue and red normals, select the red normal faces and press Alt-N and select Flip. All should be blue. Uncheck the Face Orientation checkbox. Retry the bevel.
3) Apply Location / Rotation / Scale - In Object mode, click on the object and press Ctrl-A. Apply the Location, Rotation and Scale. Tab back to Edit mode to bevel.
Hope that one of these helps.
That is a dangerous modifier if you don't have all of your ducks lined up in a row...... or the modifier stack sorted the way that it needs to be. There are lots of ways to mess up beveling in general, and not just with the modifier.
Learning and understanding quad topology better is completely critical in my opinion before one can successfully work with such a modifier. Having said that I completely understand the pains of not having it work properly. I end up just beveling on my own most days now.
I think the normals were the issue, I recalculated them and that seemed to fix it. Thank you!