emacs 26.3. 2 different builds. 2 distinct OSs.

One build is custom inside Slackware; another build is standard issue from
Fedora 32.

Results below are identical for both situations.

If the tex / latex source (or a symbolic link) resides in /tmp directory,
everything from the tex mode menu functions as expected.

If the source is anywhere else in the directory structure, the first step,
compilation (tex / latex), fails because it can *not* find the source file.
Yet, if I use my own custom elisp script or invoke the relevant commands
manually, there is *no* problem.

The builtin tex-mode.el script seems to expect all code to be only in /tmp
or nothing will occur.

Am I missing something? A variable setting? Some other configuration aspect?

Thanks for your attention.

Guido