I could find this KB article which states that this error can be caused by third party plugins:
caused by: java.lang.NoClassDefFoundError: com/atlassian/renderer/v2/macro/basic/BasicAnchorMacro
Would be possible to go to confluence administration menu -> manage add ons and click on enable plugin safe mode to disable all third party plugins and check if the issue is caused by any of them?
As you could confirm that the Word import does work for another space, the issue might be happening due to the content inside this space. For example, the Look & Feel session in the Space Administration session. Try to check the differences of it between both spaces, so you can come to a conclusion.
Another possibility could be related to the specific content in the page that you are trying to insert the Word content. There could also have some customisations.
In case of still facing the issue, in order to work with our engineers on it, please, consider raising a new ticket in our support channel: https://support.atlassian.com
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