psatkha, It simply writes "The client's game database checksum does not match the server's game database checksum. Check the installed mods and patches. Error code 0.2.0". The console is silent, and the game doesn't indicate which file it doesn't like.
I didn't have time to find out which file is causing the problem. Since GameMechanics\Creature\Creatures\Neutrals\Creature_441.xdb contains links to all other creature files, the game could be complaining about any of them.
I'll find the time to test it; it's quite convenient to do so on 2 laptops.
Added 1 hour 41 minutes ago
It turned out to be faster than I thought.
The file is \Characters\Creatures\Neutral\H5A0\Adamant_Golem-arena-cast.xdb
The line is the error; the identifier cannot be zero. I put 8506789A-17C0-4CCF-B3B1-22229B282222 there, and it worked.
I don't know how UIDs are usually generated for heroes; I temporarily copied it from a neighboring file, changing the last digits.
8506789A-17C0-4CCF-B3B1-250B9B280BD5
UIDs aren't generated in any special way; in this case, it's an internal link to the file bin\animations\8506789A-17C0-4CCF-B3B1-250B9B280BD5 - the idle00 animation, i.e., the model at rest! :smile47:
Apparently, during optimization, they cut out the internal link! :smile24:

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Неудачное планирование ведёт к неудаче ...
NCF - мод, добавляющий дополнительных существ в HeroesV 3.1