Hello

I am testing new luahbtex and comparing it with luatex because I am
considering to set OpTeX with luahbtex engine instead luatex in TeXlive
2025.
I have found a difference between lautex and luahbtex behavior which I
am unable to explain why. The difference is shown only when huge number of
fonts are downloaded by luaotfload and only with selected fonts from
internet saved to ~/texmf/fonts. And it manifests only as a little delay
(with luahbtex) during dlownloading the fonts to PDF at the end of the
document visible if you are watching at the terminal. The PDF result is
equal, but I am worried that there is a hidden bug in luahbtex because
the difference is unexpected.

I teseted this with OpTeX macros, they never use mode=harf. So I expect the
same behavior with both engines. The example for testing is somewhat more
complicated and it is exactly described at

    https://tex.stackexchange.com/questions/735071/

The main question is: why luatex behaves correctly (with no delay during
downolading fonts) but luahbtex presents a delay in given cases? Where is
the difference? Can the luatex developers explain this?

Thank you

Petr Olsak