Initially, while writing this, I didn't know what was going on. I was sure I was not modyfing the same lock in parallel, so it made no sense to me that error was concurrent modification, and I wanted to ask for help. I accidentally found out that there was another lock that was suposed to be issued with a grant at the same time, so i tried to reproduce this issue.

So conclusion is, you can't create multiple grants at the same time, even if deifferent resources are involved, I guess what was common is owner id.

Queston for tapkey team, is there any particular reason for this limitation? I wasn't able to find anything in the docs, and it caused real problems in my production environemnt.