Endnote X8 slowness problem ("lagging")

I upgraded from X7 to X8 a few days ago, the new version duplicated (very badly) many entries (but not all of them). When I delete an inappropriate duplicate (using the backspace key) I spend approximately 5 seconds watching the spinning wheel. And the slowing increases as I use Endnote

This is very disappointing and I am looking for alternative bibliography tools

Library Name: gagnevinpublis Copy2.enl
Location: /Users/gagnevin/Library/Mobile Documents/com~apple~CloudDocs/gagnevinpublis.enlp/gagnevinpublis Copy2.enl
Last Saved: vendredi 20 avril 2018 à 12:48:55 heure d’été d’Europe centrale
Records: 128
Custom Groups: 4
Reference Types Used: 4
Most Used ref. types: Journal Article, Conference Proceedings, Book Section, Patent
File Attachments: 44
Figures: 0
Authors Term List: 533
Journals Term List: 85
Keywords Term List: 381

in addition to my previous complaint Endnote X8 completely emptied one of my libraries (again just one, not all of them) and I can restore it even using a year-old backup of that library.

I am not waiting for a reply considering the other users comments, I am just now switching to a different bibliography management tool…

In my experience, when I upgrade Endnote or word to a new version (even a new update) – I often save as to make a new copy of the document, and run thru a convert to temporary citations/ update citations and bibliography sequence, as I find that the way the two programs interface may have subtlely changed.  This often fixes any lagging issues, and duplicate entries such as those you describe.  

Same problem here. Endnote X8.2 on MacOS High Sierra version 10.13.6 (17G65). But I do have huge terms lists.

Library Name: My EndNote Library.enl
Location: /Users/simonmendelsohn/Documents/My EndNote Library.enl
Last Saved: Tuesday, 21 August 2018 at 21:20:28 South Africa Standard Time
Records: 1,696
Custom Groups: 131
Reference Types Used: 10
Most Used ref. types: Journal Article, Report, Web Page, Book Section, Book
File Attachments: 1,588
Figures: 0
Authors Term List: 23,940
Journals Term List: 10,362
Keywords Term List: 21,054