Hi @Jana Melúchová , welcome to the Atlassian Community and thanks for your post.
Please open a ticket to Xray to ask for help - https://marketplace.atlassian.com/apps/1211769/xray-test-management-for-jira?hosting=cloud&tab=support . We can't see inside of your instance to be able to verify what might have happened.
They have a StatusPage but I don't see any issues there - https://xray.statuspage.io/
Best wishes
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