Follow-up: On Win7/64 & Ac2013, when I perform that experiment the font size changes and is retained (a) when I close and then re-open the VBA window and (b) when I close and then re-open the entire app.
More significant is that the change affected another database. This means that what we are discussing is a registry setting, NOT an application setting. So I got curious.
First thing of note: VBA has SEPARATE SETTINGS from the default settings for other OFFICE members. If you are comfortable with at least viewing your registry, what you want to see is:
computer\HKEY_CURRENT_USER\software\Microsoft\VBA\7.0\Common
Then you can see that "FontFace" holds the name and "FontHeight" holds the size (in points) of the font.
Exploring other items under the general VBA heading found only placeholders, nothing of importance. However, this explains a lot of things. (Doesn't fully explain the original complaint.)
If this is a REGISTRY setting rather than a DOCUMENT setting, then the question is: Why does it allow you to save an item (FontFace) but not save the immediately adjacent item (FontHeight)?
{After thinking a bit more, a significant fact is that when you open a VBA editor window, it becomes possible to have another image running in that window that isn't a child of the Access parent app window. Using Resource Monitor, the best I can determine is that some process is running under a service host or task host shell. It won't name the action image that is running, not that I needed to know, but if I close the VBA window, that unidentified item goes away. So that shows it ISN'T an Access window.}
So I figured this ought to be something someone else has seen - and it IS.
https://answers.microsoft.com/en-us...cel-2016/2f51c62d-bf74-4029-92ee-5aaebc292e39
I cannot easily reproduce the solution that appears in that thread, but the experiment is clear that somehow the VBA editor is interacting with screen resolution. I will leave it to you as to whether you want to diddle your screen resolution DOWN, increase font size, and then diddle resolution back UP to see if that changes the problem.
If that is it, I can only guess you were attempting a font size that somehow "tripped" the editor's settings as "too big" and therefore disallowed the change. Those of us who COULD make the change must not have picked an "impossible" font size. OR the problem only occurs in Ac2016 and a VBA version after 7.0