The error shown by OpenSCAD is as follows:

ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! Expr: e_below != SHalfedge_handle() File: /mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_3/SNC_FM_decorator.h Line: 426

This is triggered on Part 3 (top center of the first image below) and causes the piece to not have the maze inside of it.

It is a bit odd though, the issue only occurs on the Render step, but not on the Preview step. When viewed as a Preview, the maze is properly generated.

If JW was entered into field I or E they are not created on the generated model. Only a single J is created. If 2020 JW is entered into I the text is also displayed backwards (0202 J). Something is wrong

Dora:PuzzleBox roy$ make
indent puzzlebox.c
Error@523: Unterminated literal
make: [puzzlebox] Error 1 (ignored)
cc -O -o puzzlebox puzzlebox.c -lpopt -lm -g -D_GNU_SOURCE
puzzlebox.c:3:2: error: expected identifier or '('
2018 Adrian Kennard www.me.uk @ TheRealRevK
^
puzzlebox.c:46:2: error: expected expression
,should be less than clearance, can be - ve
^
puzzlebox.c:46:3: error: use of undeclared identifier 'should'
,should be less than clearance, can be - ve
^
puzzlebox.c:120:73: error: use of undeclared identifier 'nubzclearance'; did you mean 'nubrclearance'?
{"nub-z-clearance", 'Z', POPT_ARG_DOUBLE | POPT_ARGFLAG_SHOW_DEFAULT, &nubzclearance, 0, "Extra clearance on height of nub", "mm"},
^~~~~~~~~~~~~
nubrclearance
puzzlebox.c:44:10: note: 'nubrclearance' declared here
double nubrclearance = 0.1;
^
puzzlebox.c:132:3: error: use of undeclared identifier 'command'
command - line options
^
puzzlebox.c:132:13: error: use of undeclared identifier 'line'; did you mean 'link'?
command - line options
^~~~
link
/usr/include/unistd.h:463:6: note: 'link' declared here
int link(const char *, const char *);
^
puzzlebox.c:151:10: warning: implicit declaration of function 'strdupa' is invalid in C99 [-Wimplicit-function-declaration]
path = strdupa(path);
^
puzzlebox.c:151:8: warning: incompatible integer to pointer conversion assigning to 'char *' from 'int' [-Wint-conversion]
path = strdupa(path);
^ ~~~~~~~~~~~~~
puzzlebox.c:383:22: warning: incompatible integer to pointer conversion initializing 'char *' with an expression of type 'int' [-Wint-conversion]
char p = strdupa((char **)optionsTable[o].arg),
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
puzzlebox.c:433:36: error: function definition is not allowed here
void cuttext (double s, char *t){
^
puzzlebox.c:448:27: error: function definition is not allowed here
int box (int part){
^
puzzlebox.c:1219:2: warning: implicit declaration of function 'box' is invalid in C99 [-Wimplicit-function-declaration]
box(part);
^
4 warnings and 8 errors generated.
make: *** [puzzlebox] Error 1
Dora:PuzzleBox roy$

This code generates initials with a depth of 0.2mm but the website version generates them with a depth of 0.6mm.

I have noticed that when printing, that the nubs are quite brittle if the pieces are forced. Kids are not very gentle. I have printed another model and the nubs are stronger and dont break as much. Is there a way to increase the nub size/strength.

Here is a link to the model that i printed with re-inforced nubs:
https://www.thingiverse.com/thing:2607374

In the form on the great https://www.me.uk/puzzlebox/, it seems it doesen't matter if we change Z.

Tested with string "ěščřžýáíé". It doesn't generate the file name correctly. As a result, no scad extension is added and the file seems corrupt.

When compiling, there is a popt.h error (Windows)

When I try to render anything (i.e. standard config) with i or f and c below 21 activated I get errors when rendering in openSCAD:

The first overhang angle is too flat to be printed nicely.
My printer can print anything above 40°, the angle should be increased a little:

edit: puzzlebox-4m-3N-3H-10b-22c-50h-1B6-0G4-1w2-2t-3z-1M--1X-0p7-0g4-7s-2r-1R333333-e-Z-1T-0y1-0Z2

Thanks for the project!
Found a problem with text. First side works good. I think picture shows the problem pretty clear.