Hello Václav Řezáč,
Can it be that you need to set some values for this module in order for it to work, it looks like it needs a value that it cannot find, hence, NullreferenceException, so it can be that locally it finds this value(in the database) but in the cloud it cannot find this value.
Try to look if this is the case and why it needs it directly at deployment(maybe an after startup that you use it in?).
What also can help is to download the database from your environment and try to run your app locally with that database and see if you can reproduce the error.
If these things dont help, can you maybe provide some screenshot of the action it tries to execute
Hope this helps
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Good luck!