1.) First, avoid importing things other than articles, as ReadCube won't be even able to resolve those articles metadata anyway. Normally, once imported, articles will give you their abstract and title information while clicked in your library. They also have the potential to be enhanced, allowing you to write notes/highlight them. Without metadata, this is impossible.
2.) If you want to import all of your PDFs (including books, which can't be enhanced) move your PDFs into your ReadCube library in smaller groups. Rather than importing every single PDF all at once, import groups of 30-40 instead.
3) Leave the computer on for a day or so when you have time and turn every connector back on, making sure to check the general tab of your preferences and to check the "Automatically match unresolved articles while idle." This will take some time, so I would do this when your computer is going to be idle for a while.
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