Thickness in SHELL
Hi, that's cool you got the thickness by shelling/thickening in the outside direction. If you go to Inspect > Section Analysis and choose a proper orange plane, you can see a slice of the body as it's being thickened in the inside direction.
We see at about 1.18 mm there is a sharp point that forms inside. That is what is causing trouble for further inside thickening. So what I did was easily "go back in time" to edit the profile sketch you used to make the revolve, and I added a Fillet in that corner (incidentally I also selected everything in the sketch by clicking and dragging from right to left to make a yellow selection box, then right clicked the mouse and choose Break Link so there is no more purple geometry that was projected from your original object...this allows better editing of the sketch so we get no yellow warnings). I could then thicken inwards to your desired thickness.
Other options are of course to thicken in outward direction, and Scale the body to have desired outside dimensions, or do a combination of thickening inward and outward. But it looks like the above may be more of your original intent.
Let me know if you need more help or the new f3d file.
Jesse