Can you provide a Debug ID from the Zotero Connector for this happening?

This time it the citations became unlinked when pasted

So the only thing to toggle was "Enable Google Docs Integration". I unchecked it and still got the error. Strangely, it does not always break the pasted citation.

No, don't turn off "Enable Google Docs Integration". What version of the Zotero Connector do you have? You should have 5.0.96, and then you should have a "Enable Google Docs Integration v2 (NEW)" checkbox.

OK, we'll look into that and the original pasting issue. For now, you can turn v2 back off.

I don't know if this further confuses, or adds some useful clues:
Always, in the past, (in the v1 of gdocs integration) pasting a citation was accompanied by a short delay and a 'please wait' before the paste was complete.

Now, with v2 toggled off, I got an array of different results.
Pasting a large block of text with many single and multiple citation blocks went through without the 'please wait' or the "500 error" I thought for sure the citations would be broken, but apparently they weren't.
In other pastes, it appeared that single citations broke but multiples didn't, even with the "500 error".
Then I tested various different combos, like 2 singles in a block, 2 multiples in a block, and various others, and despite the "500 error", none were broken.

In another variation, I tried pasting and got the "500 error, (without the "please wait") but NOTHING pasted. Immediately trying cntrl-V again, the paste happened followed by a "0 google docs request failed" error, but the citations worked just fine.
The Debug ID after trying this (and other things) was D1142360415.

In sum, the paste, despite the error messages and variations, appears to be working at least 90% of the time.

The 500 error comes after every paste. Sometimes it breaks the pasted citation, sometimes not.
When you ask for Debug ID from Zotero, I assume you want the information from Tools>Developer>Error Console.
Producing the error does not add anything to the Console, and the "Errors" tab is blank.

Here some of the messages listed under "All". I have omitted some that appeared duplicative:

1656429941130 addons.update-checker WARN Update manifest for zoteroOpenOfficeIntegration@zotero.org did not contain an updates property

[JavaScript Error: "You have reached your Zotero File Storage quota. Some files were not uploaded. Other Zotero data will continue to sync to the server.
See your zotero.org account settings for additional storage options.
02699931.2016.html (821 KB)"]

[JavaScript Error: "Upload request 1/2FFYJ8ZV failed"]

[JavaScript Error: "WebSocket connection closed: 1006 "]

[JavaScript Error: "The connection to wss://stream.zotero.org/ has terminated unexpectedly. Some data may have been transferred."]

[JavaScript Error: "WebSocket connection closed: 1006 "]

[JavaScript Error: "The connection to wss://stream.zotero.org/ has terminated unexpectedly. Some data may have been transferred."]

[JavaScript Error: "Upload request 1/2FFYJ8ZV failed"]

[JavaScript Error: "Upload request 1/2CW7HH7V failed"]

[JavaScript Warning: "Error in parsing value for ‘height’. Declaration dropped." {file: "chrome://zotero/content/standalone/standalone.xul" line: 0}]

[JavaScript Warning: "Key event not available on some keyboard layouts: key=“i” modifiers=“accel shift alt” id=“key_importFromClipboard”" {file: "chrome://zotero/content/standalone/standalone.xul" line: 0}]

[JavaScript Warning: "unreachable code after return statement" {file: "resource://zotero/loader.jsm -> resource://zotero/bluebird/util.js" line: 205 column: 4 source: " eval(obj);
"}]

[JavaScript Error: "NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsICommandLine.handleFlagWithParam]" {file: "file:///usr/lib/zotero/components/zotero-service.js" line: 551}]

@aarwdc If you create a new document and insert some Zotero citations into it, then try to copy them into your existing doc, do you also get the 500 error? Can you cut down the size of the document to a small snippet, make sure it still produces the 500 error, then send it to support@zotero.org?