Since Version 1.9.2 we cannot start the LTN Manager anymore (Button in quickbar gets deactivated).
as soon as we downgrade to 1.9.1 everything works again.
(since this is a language pack it's maybe relevant: we're using german)

Language Pack do not interfere with game or mods, it's just offer translated strings for names and description of objects.
Maybe some script in other mod prevent LTN Manager function.
German locale did not changed since v1.5.1.

but it has to be a change in Version 1.9.2.
We have a running save with ~300h LTN Manager working perfect with this mod 1.9.1
-> Updating to 1.9.2: LTN Manager broken.
-> downgrading back to 1.9.1: LTN Manager works again.

Tested and able to reproduce in Single player as well as Multiplayer.
If you need any additional info let me know :)

Can you share the save file in the cloud storage?

Sure:
https://1drv.ms/u/s!AgMn9W5y29Tjg2QmlDnHaAWyeqO-?e=BN1Rij

Load your save several times, with locales EN, DE, RU and LTN Language Pack v1.9.1 and v1.9.2.
All works fine.
Button "LTN Manager" is disabled initially, but becomes available after a while (less than a minute).
This is not a bug, the LTN Manager mod needs time to collect data.

yes I can confirm this, we were just too impatient.
sorry for the false-bug report and thanks for the help.

Ok, you're welcome.
If you're an experienced player and don't mind helping out with the translation, you can do so here: https://crowdin.com/project/factorio-mods-localization
LTN Manager has almost no German translation.