I am having the same issue, working with multiple colleagues on a doc. We are all having the same issue, so it is not isolated to any one of us.
When I am not getting the error described in #4, Zotero is just unresponsive (nothing happens when I try to do something like add a citation or open Document Preferences).
Sometimes I have restarted everything repeatedly and gotten the citation window to come up. But then when I try to modify a citation there, it hangs indefinitely.
You have multiple issues which are unrelated and should be debugged separately.
If you are getting the dialog that the document is locked because somebody else is editing it - that may simply be the case, if you are all editing the document at the same time. Even if nobody is editing the document at the current time, but if they for example open the citation dialog and not close it, then sleep their computer, then another person trying to add a citation would get this error. You can override the document lock via the error dialog, although if something like I described happens, and then the person who slept the document continues to edit, you may get unexpected results or even document corruption.
When I am not getting the error described in #4, Zotero is just unresponsive (nothing happens when I try to do something like add a citation or open Document Preferences).
This can happen if you already have a citation dialog open, in which case Zotero tries to refocus it, although it may not be able to (the OS controls whether Zotero is allowed to focus its windows), so you have to look through open Zotero windows to make sure you don't already have it open. Another thing that can happen is if you open a citation dialog, but then don't finish adding a citation, and instead use your browser in different tabs, the Google Docs tab may get unloaded by the browser to conserve resources, in which case you may get a corrupt citing session which may require restarting Zotero, and may also present as the dialog about somebody else already editing the document.
Sometimes I have restarted everything repeatedly and gotten the citation window to come up. But then when I try to modify a citation there, it hangs indefinitely.
Having said all of the above, if you can reproduce this consistently, and best, in a new document where you are the only person working, we can take a look. You should produce a Debug ID from Zotero for the problem.
You should produce a Debug ID without restarting Zotero. Either way, the copy of your document would have the internal option turned on, which makes Zotero believe somebody else is editing the document, so it would exhibit the same issue. Are you saying that even if you override the lock from the error message you still get the dialog again on subsequent attempts to edit?
Yes, if I override the lock, I can usually do one thing before it crashes. For instance, I was able to open up the citation editor, but when I tried to save changes, it hung indefinitely. After restarting again, I was able to unlink the citations, so we have started again on a new doc, re-linking all the citations.
EDIT: Although I am seeing in our logs that this may be an issue related to Google Servers, so it may just resolve on its own. In the meantime you might have better luck by splitting the doc into multiple smaller snippets.
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When I am not getting the error described in #4, Zotero is just unresponsive (nothing happens when I try to do something like add a citation or open Document Preferences).
Sometimes I have restarted everything repeatedly and gotten the citation window to come up. But then when I try to modify a citation there, it hangs indefinitely.
Please help us!
If you are getting the dialog that the document is locked because somebody else is editing it - that may simply be the case, if you are all editing the document at the same time. Even if nobody is editing the document at the current time, but if they for example open the citation dialog and not close it, then sleep their computer, then another person trying to add a citation would get this error. You can override the document lock via the error dialog, although if something like I described happens, and then the person who slept the document continues to edit, you may get unexpected results or even document corruption. This can happen if you already have a citation dialog open, in which case Zotero tries to refocus it, although it may not be able to (the OS controls whether Zotero is allowed to focus its windows), so you have to look through open Zotero windows to make sure you don't already have it open. Another thing that can happen is if you open a citation dialog, but then don't finish adding a citation, and instead use your browser in different tabs, the Google Docs tab may get unloaded by the browser to conserve resources, in which case you may get a corrupt citing session which may require restarting Zotero, and may also present as the dialog about somebody else already editing the document. Having said all of the above, if you can reproduce this consistently, and best, in a new document where you are the only person working, we can take a look. You should produce a Debug ID from Zotero for the problem.
Since the error recurs in a copy of the document, I don't think it's probable that there is actually another user causing the issue.
EDIT: Although I am seeing in our logs that this may be an issue related to Google Servers, so it may just resolve on its own. In the meantime you might have better luck by splitting the doc into multiple smaller snippets.
https://forums.zotero.org/discussion/108606/google-docs-issues