Close CodeBlocks.
In AppData there should be a CodeBlocks folder and there a default.conf file.
Open it and find something like
<TOOLTIP_FONT>
<str>
<![CDATA[Comic Sans MS 8]]>
</str>
</TOOLTIP_FONT>
Delete this, start Code::Blocks and report if it fixes the problem.
Also remember the setting and post it here.
I have done everything you suggested but it has not fixed the problem, in fact it has made it slightly worse, as the value 1234567890 is now displayed as 1234567, a digit shorter than before.
The text is visibly smaller in the value window that does display text (the reason I changed to Calibri 10).
I located
C:\Users\David\AppData\Roaming\CodeBlocks\default.conf
and made a copy before I deleted
<TOOLTIP_FONT>
<str>
<![CDATA[1;9.75;-13;0;0;0;400;0;0;0;0;3;2;1;34;Calibri]]>
</str>
</TOOLTIP_FONT>
Should I restore this code, or would uninstall and reinstall CodeBlocks be likely to fix the problem?