Most likely the lxUseCell parameters are out of date on the cells/blocks in the schematic . Either remove it or have lxUseCell point to the correct location, you will see it in the query form under 'User Properties' (I think
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In case you are not aware of what lxUseCell is for, it is used to tell XL to grab a layout from a library other than the library that the schematic exists. You may not be pointing to the library that was originally used, hence it cannot find the layouts necessary to continue and imports nothing.